There will absolutely be a big esports following for PC Halo. Bet you any money, a lot of Halo pros that play on console may even switch over to PC. A lot of pros that had roots for esports started with Halo on console, and then moved to PC in some way, and now play Siege or Counter-Strike on PC, of course, assuming they started on console. Usually esports gamers that start on PC started with Counter-Strike, but if they start on console they usually came from Halo, and my guess would be those who started with Halo and then went to PC will go back to Halo on PC.
For example, Ninja started with Halo on PC, and now he plays PC games professionally for Twitch, mainly Fortnite.
I have high hopes for esports for PC Halo anyway, but maybe I'm wrong, but I highly doubt it.