Lower tiered and higher tiered alliance raid would be a good idea.But to make it effective you'd need to lower the rewards for the lower tier and give higher bonus for higher tier to encourage people to engage in the higher tier one or both.
I think though the real problem is sync down maximum ilvls need to be balanced.If people werent so overgeared in lvl 50 alliance raids they'd probably think twice about gear switching as the lvl 50 ones you'd be forced to have to do mechanics.