LFR is too popular to just abandon it. I like the idea of fixing it to run with NPC's rewarding gold, transmog or some of whatever currency is current. That will detoxify it and put an end to the developer's attempt to delude people that LFR is raiding (it isn't). Of all the difficulties that run in raiding content this is the easiest one to keep.
Consolidate Normal & Heroic. Scrap Mythic and return it to just like it was when it was heroic in Wrath sized at 15 (with some flex for when teams start to outgear it).
For World First—which Blizzard hilariously says they don't support—create a World's First version of the raid that runs at Mythic difficulty (or harder), call it Tournament Level, make it available and use it only for World First and regular tournaments. Leaning towards that being 10-person teams.
Gearing for all non-LFR content should be done through Mythic+ and lower difficulty versions of the raid.
Or just leave it alone. I think raiding is OK right now for raiders but this might shake things up in a way that would be interesting.