Screenshot of the new Piloting tree:

First tree is the 'engines' tree, focuses on one of three paths: equipment unlocks, maneuvering, or raw/cruise speed and 'specials'. The second tree is the new hull tree; the weight classes are corvettes (previously the frigates), frigates (mid-size) and cruisers (the slow beasts like before). Each has a basic, advanced and elite category to them with basic and advanced more or less corresponding to the old 'light/heavy' split. Ergo, for the variants I did on the Banshee hull:
Athena C - No requirements since it's the civilian version.
Athena Mk I - Basic Corvettes
Athena Mk IIB or Mk IIE - Advanced Corvettes
Athena X Experimental - Elite Corvettes.
High performance ships like the bomber (Fang) and gunship have no civilian model, so they simply start out requiring Advanced Corvettes.
It should also be noted that when I release BTC 0.95, there will only be 3 frigates (miner, the multi-purpose Orca refit, and the tanky-as-hell Crab refit) and only one cruiser. Still, frigates open at level 5 and cruisers at 10, so people wanting to fly larger boats won't have to wait nearly as long in the scheme of things, though as one might expect the cruiser you can fly at level 10 isn't on the same level as a Hammer or Deathbringer in vanilla.

This also provides for a natural level of hull unlock progress. Level 1 is basic corvs, 5 is basic frigs, 10 is basic cruisers, 15 is adv corvs, 20 is adv frigs, 25 is adv cruisers, 30 is elite corvs, 35 is elite frigs, 40 is elite cruisers.