I don't want to bust your bubbles, but there are many free games on Steam, much of them I've installed, played for few days and forgot about them.
Even if TB gets greenlighted, it will not miraculously 'change' into something else over night, it will still have same problems: compatibility with other OSes, bugs and glitches, lack of tutorials, steep learning curve, specific player base, etc..
Standard Steam customers are demanding polished product, even if they doesn't have to pay for it.

We are all hoping for the best, but we must also be honest and try to see Tb through the eyes of someone who doesn't know about TB forum, installs the game for the first time, encounter totally strange and specific gameplay not knowing exactly what to do and where to start.
You must invest much time to get to like TB, and ppl on Steam doesn't strike me like that audience. Some numbers will rise, for sure, since this is the first mayor game promotion for a long time, but I don't expect thousands and thousands of ppl swarming Tb servers all of a sudden.

Might be that all will stay less or much the same.
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And just to add, I recommended TB to at least 10 of my friends hoping to play it with them. Out of those 10, only I have played it. With an emphasis on played it. This game is strange. Either you like it on the 'first ball' or not.
1 out of 10. :]