WGI recently began doing indoor brass as well. BK's been doing it for years... I think the first time I remember seeing them was around the first time I auditioned for the very first time, and that was way back in 05. They're expanding now.
At any rate, I know a ton of horn players who have not only fallen in love with WGI, but have managed to get involved. Cymbal players can be pretty ######, and that's the way a lot of wind players find their way into WGI. Or they do guard. Hell, I know next to nothing about guard, but during WGI finals even I get hyped to see the world class groups perform. It's theatrical and beautiful.
Drumlines have much more theme-centric shows than DCI. Anyone who says that DCI is trying to move towards WGI is probably right, but it's a cheap punchline, because DCI will never be able to come close to what WGI has managed to do in terms of theatrics and thematics. Tarps, props, drill, and music are all very meticulously integrated into shows. There have been very few DCI shows where I've thought the props were little more than, "hey, this is what our show is about!" and then they just kind of serve no purpose aside from that.
It's not a knock on DCI (or DCA for that matter) at all. They're simply different activities. But as someone who had experience in both, I can honestly say that WGI caters to anyone who cares to give it a shot.