Hey, I used to play endless legend 1 and recall really enjoying it so was surprised and instantly interested when EL 2 news popped into my feed.
Tidefall especially seems like a great way to keep things about the environment/map being fresh and providing new opportunities throughout the game. Most 4x games usually have a pace where the map feels mostly discovered and locked in about mid-way through the game. Generally borders are largely determined and any further expansion necessitates conquest, Ruins are all taken, all AI factions are met etc. So hopefully tidefall can keep the exploration component of 4x interesting throughout.
However, some forseeable consequences do come to mind:

1. Are starting positions going to be naturally isolated by surrounding untraversable waters. If so, that seems like it would favour economy focussed factions and hinder conquest focussed factions. Economy factions get to build without threat, conquest factions have access to fewer... "resources" to capitalise on (thinking specifically necrophages who appear to be in EL2 and in EL1 amassed food stockpiles through unit kills). Conversely, If the conquest focussed factions have access to economy factions on small inescapable land masses, good luck I guess? Have these balancing concerns been considered and addressed?
2. Another balancing related consequence: If the waters are receding, presumably that means the starting positions, most likely the positions of the capitals of each faction, will all be on high ground later in the game. Every battle that will be fought trying to approach a factions capital later in the game when the land bridges to do so become available; will have to be fought uphill which I assume gives some kind of stat based combat advantage. If these assumptions are correct, won't any domination victory type put the pursuer at a natural disadvantage and favour factions that can turtle and build tall well?
3. Will there be any place for a naval component to the game? As in, many 4x games have ships to wage war with or in the case of EL1 Tempest engage with fortresses/sunken ruins. The naval component normally would have your capabilities and the utility increase with technology unlocks. Though if tidefall means ever diminishing oceans as the game proceeds, then surely the relevancy of anything naval would also decrease?
4. One of the main deviations to norm I thought might come out of tidefall is the introduction of uncontested land to settle later in the game, allowing for an alternative to the usual conquest. However, cities settled later in 4x games can often take a while to gain relevancy and be worth the investment as opposed to already developed conquered cities, especially if you're not boosting them through an empire wide resource like dust/stockpiles. Should earlier (tech wise) city infrastructure become cheaper to build the more progress down the tech tree a player has made? Should border expansion (if that's a thing) and city growth be boosted until the city reaches closer to a game stage average? Is it even an issue? I don't know. Like I stated before, usually expansion opportunities through settling your own cities late game is not really a thing. Most recent example I can think of was playing a civ6 game with a friend where the only late game city I settled was on a single land tile island in the middle of the ocean just because it had 3 oil resouces near it. It's purely done to gain access to strategic resources and the city itself couldn't ever amount to much. Will late game city settling in EL2 be similar or has this been addressed already?

I suppose there's no chance of getting any of these answered since that'd probably be spoilers / leaking information. Though maybe they are useful questions for devs or insiders to mull over if not doing/done so already. Perhaps fun for everyone else to speculate on and suggest other things tidefall might foreseeably impact or propose solutions to or present reasoning for why they are non-issues. For instance, for number 3, I thought it would be cool if at some point in the tech tree, your ocean based naval units could upgrade/transition to aeronautical airforce units or gain the ability to switch between those traversal methods. Air units / transport also potentially circumventing the hypothetical issues of terrain advantage raised in question 2. Seems to me factions living on a planet that became increasingly more mountainous, with their main strongholds atop mountain peaks would want to figure out some form of air travel pretty quickly. Also hyrdothemal vents becoming exposed possibly could translate to updafts for gliding style airships or balloons. It's a fantasy setting though, so could just as easily be large rideable sea creatures turn out to be able to or adapt to fly and technology unlocks harnesses or techniques enabling their stewardship and mounting. Maybe too late in development to add anything like that if it doesn't already happen to be a thing but who knows, dlc some year or 2 later? Anyway just wanted to share some thoughts when thinking about how tidefall could change things up.

Well, yes

​​The trailer showed UE and necrophages 2.0 approaching each other on the same island in the global map, so unless it was a situation deliberately constructed for the trailer, that does imply factions will be able to travel between islands before land bridges form. It wouldn't surprise me if conquest factions have access to ways to island hop more easily, letting them rush other factions. For example the Necrophage 2.0 could have a mechanic similar to the mykara's tunnel construction and just burrow to new islands bypassing any navies for all we know.

Fortresses have been mentioned by the devs in the reveal stream, however they are apparently don't appear until after the first tidefall. I'd assume since they have the same name, they work like the endless legends 1 fortresses so there will be a naval component, tho i guess they could just be a special type of ruin in the new lands? That said if they are the endless legend 1 type of fortresses; i wonder what happens when the sea region with a fortress in it becomes affected by the tidefall. Will you still own the region? Or will the fortresses effectively become ruins, unsettleable tiles that grant unique yields? Or will they function like the Kapaku's golem camps and effectively be isolated disctricts letting your cities in the region get a quick start?

The devs said they wanted each tidefall to introduce new mechanics and resources, so i assume the late game strategic/luxury resources are only found in the deeper regions uncovered by the tidefalls. Could mean that only those who settle the lands revealed by tidefalls in the late game will have access to mithrite and hyperium and that weapon technologies will be time gated to an extent. So your Civ 6 oil example might be similar to what we see, a sort of gold/oil rush to expand for the late game resources.

The devs also mentioned in the reveal stream that the second tidefall causes "Doom-wraiths" to appear. Perssumably the doomwraiths exist to mirror the minor faction villages becoming hostile in the second winter back in endless legend 1, since someone else on here speculated that minor factions wouldn't be hostile in game 2 since the devs were suprised by the minor factions being hostile when they streamed endless legends 1 after the reveal of game 2. Either way, the areas revealed by the tidefalls might not be as uncontested in the late game as we think.

Here's the link to the reveal stream: https://www.youtube.com/watch?v=SLr5mSN7Rts , the fortress and doomwraith stuff is mentioned in the first 5 mins.