What are your thoughts on loot distro for classes that dual-spec during raids? Use dkp, or main spec rolls (but what is main spec now? and is it fair to classes who likely won't change specs? (ranged dps mostly)
It really depends on how your guild handles loot now. The guilds that run on pure DKP probably won't change anything. Pure DKP systems don't disadvantage pure DPS because the hybrids purchase more items, which tends to keep their DKP lower than the pure classes. In my experience, pure classes usually have more DKP than hybrids of similar attendance.
However, guilds with a priority system in place will probably have their members declare a main spec, and use that to determine who gets what. They may add a new level to the priority scheme. For example, "main-spec > off-spec > alts" might become "main-spec > 2nd-spec > off-spec > alts". But they may not, feeling this is more trouble than it is worth.
If you're really min-maxing, say with a Loot Council, you may see gear distributed with an eye to how much time is spent in each role. For example, pure classes might get preference on DPS gear because they will use it 100% of the time. Tank/DPS hybrids might get preference over Healer/DPS hybrids because it is more likely that a Tank will need to switch to DPS for several fights.
I don't think dual-spec will really change loot distribution though. Most hybrids already pick up multiple sets of gear under current systems, and I don't think it is worth the effort to formalize it.
It might cause drama in PuGs. PuGs will probably have to declare what type of loot they are looking for at the start of the run, as a DPS-main might be switching to healer just for this run, but would still want to roll on DPS gear.