A lot of my optimism admittedly comes from my desire to see it passed. But, objectively, as far as firearm legislation goes, the performance of the HPA in the past year has been stellar, picking up more cosponsors, faster, than pretty much any pro-gun bill in recent history.
Add in to the fact that the ATF has said outright that they won't fight against the HPA and indeed the recent white paper that was "leaked" indicates that there are strong feelings from inside the ATF about taking them off the NFA on their own. Of course, the white paper isn't policy, and obviously those feelings aren't universal. But it's good news all the same.
On the financial side, I'm not sure how much money is actually generated by the tax stamps or where exactly it goes, but in total I can't imagine it being a significant amount as far as the US Government is concerned. Millions to be sure, but against a budget measured in the hundreds of trillions (on which we don't seem to give a shit about being in the red every year as it is).
Plus...Trump Jr is all about the quiet pew pews and is close to some industry people. Trump himself also proclaimed himself to be adamantly pro 2A during the elections and it's an opportunity to prove that such proclamations were more than just lip service.
I think, all considered, the conditions simply all line up really well for the bill getting passed. Maybe I'm wrong in the way I've read things, but I'm hopeful and mostly confident that I'm right.