I'd just like to say something real quick. Here are CS:GO player stats from when the scene started to take off:
http://i.imgur.com/BUBCYkk.jpg
Notice that in November 2013, the game had already been out for several months, and had roughly stagnated at an average of 29,000 players. For reference, TF2 has been steady at 50,000 average for a while now (yes, even after Overwatch). The first spike in playerbase in December 2013 came with the first Valve-sponsored major, Dreamhack Winter 2013. From then on, the playerbase steadily grew with spikes every 3-4 months with each passing major.
A valve-sponsored tournament would go farther than anything else when it comes to growing TF2. I'm not sure if it will ever happen, but if it does the scene will become larger and stronger than ever.