Mostly a note to myself (and anyone who wants to take a stab at things):
Shadows - Summons and summon boosts
Gaps - Counters and strikes
Phantasms - Buffs, changes in the world, illusionary terrain, storms, etc. Most AoEs.
5 Thresholds at each type/level combination - so 5 level 1 gaps, 5 level 1 shadows, etc.
1 Base Class
5 Prestige classes
Once the basics are in place, I'll see about turning it into a full 3 base system.