Let trusts flex at least one other role
i like trusts but i don't like being pigeonholed into having to play x role to most efficiently level them
for example in the mothercrystal urianger is able to also function as a dps.
now how i'd do it is have it is keep it within the same/similar gameplay style (for example, have alphinaud flex as a caster since he's a healer, let thancred function as a melee dps and estinien as a tank)
more flexibility would make things a lot nicer and grant you flexibility so you can play what you want without worrying about other characters falling behind