Summary: too much money in PC tournaments compared to console tournaments and console players are getting tired of being paid less for putting in same amount of hours to practice and want that PC/CS:GO money
actual post:
I actually think in the next year or two COD competitive play will swing back to PC from consoles. More tournament type buildings are popping up across the country in MLG style but they only support PC gaming (because league of legends, dota, CS:GO and hearthstone are so big in competitive scene - regardless of peoples personal opinion about them). Nadeshot started playing H1Z1 and CSGO on PC and even he kind of admitted call of duty competitive scene has been dry the past 2 years or so (it was almost a fad type competitive scene for consoles).
Believe it or not, PC had as long of run competitive wise as far as tournaments go than consoles did for Call of Duty(call of duty1-4), so its kind of already pre built in. The main difference is that on PC you can edit server files to cater to competitive crowd where on console you pretty much have to play whatever the creators of the game put infront of you.
if BLOPS3 does not bring it back to what it once was competively or even further (it needs to be a featured game at Dream Hack, ESL, etc.) then I think thats it competitively for call of duty unless they bring it back to PC to get real sponsors and money behind it
sales wise I dont think itll ever swing back in PC favor though. Too many young kids play it and most of them not about that PC life.