A fight with Tom is already massive at this point. Thinking there won't be hype is utterly foolish.
From purely a hype standpoint to casual fans (which is what translates to $), it's fair to say that a fight with Pereira will be bigger IF Alex wins and looks great tomorrow night. But the reality is that both fights would be huge, and there are other factors that should be taken into account. Tom isn't just the interim champ--he already defended that belt once. So, how much do you want it to look like an actual sport? If you're creating interim titles and then having the clear next guy win that interim title and be skipped over TWICE to allow the champ to cherry pick easier and/or more lucrative fights...you stray far away from legitimacy. Which...some people are fine with.