I Like where this is going, actually i tried to houserule multiclassing as well but never reached any solid ground, So, i was thinking, instead of giving full class benefit (At a max of x1.5 lvl), I would limit the benefits to the essence of those classes i.e:
Barb: Rage/rounds / uncanny d.
Bard: Bardic music/rounds/spellcasting
Rngr: Fav. enemy (??)/spellcasting
Ftr: weap. training/ Armor training
Mnk: AC/Flurry prog/move.
Pal: Smite evil (? or Maybe LOH)/spellcasting
Rog: Sneak attk/uncanny d.
What do you think?
Full Spellcasting classes, gets the caster lvl, Partial spellcasting enhaces some of their abilities and a bit of spellcaster lvl. And martial classes enhaces their abilities.-