Would be awesome if we could research retrofits of our lower tier ships, considering plenty of "flavor" ships are being added in the earlier tiers for the C-Store, and are pretty much useless unless you want to stay Lt forever.
The problem is I dont think there would be any way for a crafter to 'sell' a retrofit ship to another player. Not everyone does crafting - in fact, a very low percentage of overall players do any crafting after the initial memory alpha mission that teaches you how to do it. I havent done a single bit of crafting on any of my characters - hell, an active fleet is lucky to have 2-3 maxxed crafters.
If crafting is a method to obtaining retrofit lower tier ships, it should not be the only method - offer the same ships via emblems, free ship purchases upon reaching the rank of vice admiral, and on the c-store.
Still, I'd give anything to have my heavy escort with t5 capability. That topic is one of the most responded to in the escorts subforum and on the cstore forum, and I see no canonical reason why the akira/zephyr/oslo could not function alongside current t5 ships.