I’m sure this has been pointed out before, but group loot in LFR makes collecting transmog painful for everyone involved.
The optimal way to do it at the moment is to never do any higher level content that award raid gear, including Timewalking and M+ bonus events, so that you’ll always be able to roll need on what you want. Alternatively, you can go in and roll need on everything possible (even if you don’t need it) then hope you can trade it for the transmog you want but weren’t able to roll need on. Both are horrible options, because this means that well geared characters are disincentivized from queueing up to help things run more smoothly and the ones that do will want to roll need on anything they can just to trade it later.
Since people have been asking for a long time now for higher level pieces to unlock the appearance of their LFR equivalent and it’s still not a thing, I assume the devs don’t want to just hand out appearances and honestly I don’t entirely disagree with that.
So I think another solution would be for the revival catalyst to let you convert a piece for free if you have a higher level version of it, immediately instead of after the season ends. This way, you still need to find an item of the equivalent ilevel to convert instead of the appearance just being handed to you. Of course, this does nothing for hunting weapon appearances, but at least it would be a start.
Another, and the one I’d prefer, would be to let you sign up to LFR specifically for transmog. The way I envision it, you would be locked out of rolling on any actual loot against other players but each boss would go back to personal loot for you and have a chance of dropping a purely cosmetic version of any transmoggable loot they could normally drop (so no trinkets, rings, necks). Alternatively, it could just immediately add the appearance to your collection so that cosmetic versions of every item wouldn’t have to be added. This would encourage well geared transmog hunters to run LFR without being in competition with the people that are actually there to gear up.