Well, lo and behold:
Chris Perkins speaking at Hame Hole Con 2015 said the following, and I think this might be even more true than it was then:
Home-brew vs. published -- A great bulk of those who play D&D run homebrew settings. But of those home-brew campaigns, over half of those homebrewers do pillage from other settings ... 15% or 50% of the world they've created has hawked stuff from other worlds. They're comfortable pillaging our products for ideas. That homebrew number, I can't remember the exact percentage, but I think it's like 55% homebrew. And then it's like 35%
Forgotten Realms, and then everything else ... Very few people right now, turns out, running
Dark Sun campaigns. A sliver of a sliver. Very few people running
Hollow World campaigns. Very few people are running
Mystara campaigns. It pretty much goes Homebrew,
Forgotten Realms, I think
Greyhawk's at 5% ands then everybody else is at 2% or 1%.
Chris Perkins from Wizards of the Coast spoke at Gamehole Con 2015 and talks about WotC's different release schedule and hints at an upcoming product!
gamingandbs.com
WotC's Chris Perkins, Principal Designer for Dungeons & Dragons, was at Gamehole Con a couple of weeks ago. He took part in a panel there in which he covered a lot of things - product schedules, partnerships, other worlds, story flavours, staffing, upcoming storylines, Greyhawk, and so much...
www.enworld.org