Allow ships to be upgraded to any design of the same hull type

This would be great, and simpler for Amplitude to implement than the other idea. I hoped for a similar ability to be added in Endless Legend, but it didn't happen.

For example, when I am low on strategic resources I could build ship designs with industry-only modules. When I have some strategics, It would be easy to tell which ships need upgrading. (No need to mouse over all of my ships to figure out whether its the Slicer2 and Slicer5 ships that should be upgraded, or the Slicer3 and Slicer6 ships).

I would love to see this. Note that it is significantly easier to design/implement and more flexible for the player than the "retrofit tree" idea linked above.

• Design issues: None. A complete loadout change within ship classes is already possible without penalty by changing a single design around. The AI makes extensive use of this; it is merely inconvenient for the human player to do so.
• UI issues: A button to trigger the new functionality and a menu to select the target design would be required. These elements could clutter the main UI.
• Engineering issues: As described above, arbitrary equipment changes within the same class are already implemented, particularly regarding costs. This idea could add the requirement to change any notion of "current design" associated with a ship in the game's data structures.

To avoid clutter on the main game screen (where the upgrade button sits), I propose to add the general retrofit funtion to the fleet section of the military screen only. This screen already allows the selection of entire fleets and individual ships, like the main UI. As mentioned above, it would require a button to trigger the new function and a way to select the target design.

The current upgrade button is referred to as "retrofit" in the military screen. Its icon is a double hexagon (stylized cube?): . By contrast, the main screen adds an up arrow to aid understanding: . I propose to adopt and embrace this distinction on the military screen:

The "Retrofit" button would be active whenever only ships of the same class (hull type) are selected. Clicking it would open a selection dialog for the target design.

The main screen UI would remain as it is, with quick access to the standard upgrade function.

PS: As this is largely a user interface issue, OP might consider adding the "GUI" tag.