Here is a list of all of the generic unit upgrade paths and the CS of all the units up to the end of the industrial era.

Land Units

Ranged/Gunner path: Archer (16), Crossbowmen (31), Arquebusiers (39), Musketeers (46), Line Infantry (47)

Melee: Warriors (17), Swordsmen (25), Great Swordsmen (35), Halberdiers (41), Line Infantry (47)

Anti Cavalry: Spearmen (20), Pikemen (31), Halberdiers (41), Line Infantry (47)

Heavy Cavalry/Gunner Cav: Heavy Chariot (22), Knights (36), Dragoons (46)

Pathfinder/Cavalry: Scouts (13), Horsemen (26), Same as Above

Cavalry: Scout Riders (16), Same as above

Stealth: Saboteurs (31), Partisans (45)

Heavy Weapon: (Dhanvi-Gaja upgrades into this tree), Mortar (40), Howitzer (49), Siege Artillery (51 and can perform bombard actions), 

Gunner with suppression: (upgrades from some elephant unique units and the Ming Rocket Cart)  Heavy Machine Gun (50 and the unit it targets can only move or attack next turn but not both) 

Naval units 

Boarding Vessel/Gun Platform: Pentekonter (22), Quadrireme (28), Cog (33), Carrack (39), Steam Frigate (51)

Naval Transport: Transport Galley (18), Caravel (37)

Gun Platform/Armoured Vessel: Man O' War (53), Ironclad (54 but +11 when in coastal waters)

Boarding Vessel/Torpedo Vessel: Privateer (40 and appears as a neutral vessel so doesn't incur grievances), Torpedo Boat (50 and strong against ranged attacks)

Air Units

Fighter: Biplane (51 and can perform bombard actions)

Thanks to everyone who helped make the Humankind Wiki; it helped me put this list together very quickly.

So I have a few observations:

1) Most of the units you'll use in the game will upgrade to line infantry which is slightly boring and an incredibly weak upgrade for the musketeer

2) dragoons are the same CS as musketeers despite being from the next era, though you could probably argue that this is offset by their ability to move before and after shooting. What do you guys think?

3) Why shouldn't scouts upgrade into scout riders? It would eliminate a second upgrade path that feels unnecessary, though I suppose it might be that way since it would be silly to be able to spam a million scout riders on turn 20 or so just by upgrading all the units you got during the Neolithic era.

4) The fact that no generic unit upgrades into the heavy machine gun, forcing you to take elephants or the rocket cart if you want the option is a cool idea, but it might be nicer to have musketeers upgrade into them so that they can have a more satisfying upgrade path and we can increase the prevalence of units other than line infantry in the industrial era.

5) The Man O' War has extremely high CS, higher than almost anything from the industrial era, and it upgrades into the scariest unit I've seen in the game so far, the ironclad (54 CS on ocean tiles and 65 CS on shallow water tiles). The Man O' War is also higher CS than the Steam Frigate which is basically a Man O' War but with a steel plate around it... that doesn't feel right. I know that the Man O' War doesn't upgrade into the Steam Frigate, but it makes the second promotion class of gun platforms absolutely useless. I think a bit of a nerf is warranted for the Man O' War and Ironclad. I would say probably drop the Man O' War to 48 or 49 CS and only give the ironclad +6 in Coastal Water instead of +11

6) Biplane and siege artillery are both pretty weak compared to the higher CS stuff that came before them on the tree, but I guess that's fine since they have the ability to bombard tiles.  

Obviously the unique units completely change the game and offer interesting counters to certain units, but I still think that there's some weird pacing issues with CS of generic units in the current build.