I'm all for trying new things on navy. Perhaps we can make some test mods and try these things out. I won 2nd place in the unit design competition last year, my beautiful Shaman mk 1 losing to a CLEARLY INFERIOR cybran "yet another attack bot" and I'm not salty at all... Because made it in 24 hours. Anyway, I can modify the ships easily and have been studying naval history and theory to hopefully make my own naval RTS games.
Amyway, presuming we are only altering the one unit I would say the shard should stay at sea. The Aeon theory is kinda laser focus on one aspect or strength, requiring further thought into platoon composition and balance, or something like that, IDK.
In my mind, a unit that performs well enough to be a viable AA component into T2 or maybe even 3, would be ideal. My pet idea to make this so is changing their weapon to an instant travel laser, with a bit of flak. Instant travel means it can. Hit all tiers of units, a bit of flak means it's a bit more useful for a bit longer. That might make it too good though, depending on the numbers. I do think that this could make it a suitable supplement to cruisers as well.
Though in my mind if I were redoing the whole thing the thing called "Attack Boat" (The shard), would be some sort of viable attack unit. Low HP attacker or something. With the frigate having the AA, and a 4th new ship filling the role of a "Monitor" with a shore bombardment role in T1, which I presume is what the 2 extra range on the Aeon frigate was meant for.
Anyway, I love the naval part of the game. Hate to see a 3d model and whole unit go underused.