Concentration-gating. What do you think?

[NichG]

I'd do two (different) things:

- The recipient of a buff has a number of slots equal to 5+Cha mod worth of spell levels they can support. Debuffs don't have this limit or interact with those slots. A buff recipient can take over Concentration from the caster (see below) with a Spell craft check DC 10+Spell Level, but failure ends the spell. You can take 10 on this check.

Optional rule: debuffs also use these slots, CL check against existing spells for a new one to displace an old one. Reason to want Cha 4, so you're immune to debuffs at 3+ spell level, but a bit silly.

- The caster of a non-instantaneous spell may *always* choose sustain it via 3.5e Concentration, which means they must spend an action (maybe reduce to swift?) each round they want to keep it up and it risks being disrupted, but the duration doesn't count down. If concentration is disrupted, the spell ends. If the caster lets go, it's normal duration begins to count down. You can't re-engage Concentration once you've let it go, and Concentration is needed in order to change any ongoing parameter of a spell on the fly - so this probably hits any non-freewilled summons and maybe even Dominate Person.

Mostly the idea is to make precombat buffing a bit simpler (no 'guess how many minutes until the encounter'), and to have a bit of an elastic 'how much magic can you bear', making Cha and even Int have additional tertiary relevance even to noncasters.