Yeah, I don't think TF2 will go far. Only Jeff and Dan really got into it, and even then Dan fell off. Jeff cannot and will not fight for both Doom and TF2.
I really doubt that Jeff will have to fight for Doom at all. TF2 has an underdog factor that I think will play well in its favor -- people that didn't play it will just want to reward overlooked gems sometimes, and won't go toe-to-toe with Jeff.