A skipjack in 1/48; a hoy in 1/32, perhaps cutters in 1/72 or even larger. Tow boats, pilot boats, fishing craft--how about a Buoy Tender?
Larger scale, simpler rigging, big but not too big--interesting subjects to engage the interests of modelers. Not drive them off to cottage and aftermarket sources.
A 1/48 Hoy would be about a14" hull. One mast and a top mast; gaff, boom, and maybe a topsail yard. Less than an whole extra sprue would allow making into an Anchor Hoy. A Water Hoy would just need barrels. A Ballast Hoy would just need a derrick and a clamshell. A Gun Hoy would need tie-down bolts for the gun carriages.
A cutter would be similar--used by just about everyone in the Leeward Isles--you could legitimately claim one was Dutch, another British, and even American, and only change the box art a bit.
A brig hull could be easily repurposed as a Snow; or a Brigantine. Design the bulwarks right and the kit manufacturer could offer a mercahntman or an armed version. Just a few changes and a Bomb sloop/brig would not be a stretch.
Just how many 1/48 U-Boats are going to bought, let alone built? And we can't even get a brig or a hoy.