Eh, FL was kind of the extreme bad scenario of how not to do trash epics. T11 did it pretty well (even if there was barely any trash in BWD to drop epics).
For a guild that would be clearing the bosses, trash epics provide a way of breaking up the monotony of trash clears. Something shiny drops, everyone goes 'Ooo', and it's a little more interesting than 34 silver, 21 copper and the tail hair of a Corehound.
Sure, FL was a bit dumb with the ability to solo trash for tons of gold. But the easy way to solve that is to put the majority of trash behind a boss: that'll get rid of most people's ability to solo trash. Sure, some can just use an in progress raid ID, but it'd still prevent the majority of trash farmers. And of course, making the trash run at 300% run speed so it can't be kited.
I suppose it's a case of 'don't ruin it for the majority because the minority abuse it'. It could also be a case of mixing it up a bit, so we don't always know exactly what's going to happen. Sometimes we'll get trash epics, sometimes we won't. That sort of thing.
All they need to do is give the trash an ability that if they don't strike something with a spell, or melee effect after 10-15 seconds, they pull their target towards them. Like a death grip, so your bound to get hit atleast once every 15 seconds, so it'll be pretty tricky to out last it against mobs who take a while to kill.
BoE epics from trash done right is fine; make it very uncommon (but not damn impossible to find like how patterns became in FL) and it gives a reward to raiders to use/sell (as raiding is expensive, a new boe can easily bring in revenue for a GB). And even if "casuals" go in there just for some hope of drops, hey at least they're raiding, which is what blizz is trying to get people to do. It's either that or they go afk in BGs for several hours for HP and maybe some CP for "easy" epics. And personally, I'd like to limit the dumbass afkers and bots in BGs compared to the ideal some casuals are off in DS.
I actually quite liked the FL trash drop system with the firestones (patterns are impossible to get though it seems). Only problem was that combining the low drop rate of firestones and the BiS-ness of multiple items made it quite stupid. An item like staff of scarlet pain was nice though: same ilvl as boss drops, but no socket and crit isn't what most casters aim for, so there's always a chance to get a(n small) upgrade from bosses, both on normal or heroic. Cleavers was stupid for dk's; at least on heroic, on normal you can just buy them I guess but hoping on firestones quickly seemed quite frustrating.