Failed to load mods: Technology steel-plate-productivity: Infinite research followed by level 6

That is all that comes up when you try to launch the game and pretty much all default mod settings on EPR

Can test by just loading K2SO and its dependencies with EPR

That's a tricky one. The quick and dirty solution for you would be to load the game with only EPR, uncheck the "Adjust existing productivity techs", then add K2SO. This should make it possible to run the game and you only "lose" the early levels of existing Space Age productivity techs being cheaper with EPR.

The main problem, however, with Krastorio 2 is that the philosophy - as far as I understand it - is that early tech cards should get phased out after purple/yellow science. EPR does the opposite. I'll need to add a different logic for K2 games that changes the base progression EPR uses. I'm not sure right now, when I can implement this - mainly due to my limited time, not because it is impossible.

Apparently K2SO automatically removes obsolete tech cards from all technologies, so I didn't have to change my logic after all. I just left steel plate productivity alone. I'll need to revisit the topic to fully incorporate EPR's changes into the tech tree, but for now it's good enough IMHO.