Ah, good to find out that we can at least put mark 10 items in the older ship slots, that helps some without making the later ships not worth upgrading into.
I dunno why I had the notion that I could not put mark 10 for example in a heavy cruiser, good to know. I might have tried it in beta and it didnt work then and got it in my head, I cant remember how I got the idea that it wouldnt work. I shoulda just given it a try I guess.
It will be less efective, but I wanna have fun seeing what an older ship can get away with.