I suspect you'll find in practice that you end up being above the PSF for most of the season if you indeed stay in D. III or promote again to D. II, looking at the other teams in your league. But, there's no requirement that you do so.
I was never in D.II, I'm very new to this game, and I'd be shocked if I promoted this season with my current roster. If I did, however, I would pretty much be forced into buying a stud or two from the market.
All in all, I like the change, but for those who want to increase the salary floor even more, I say it would hurt home-grown teams too much. (And I despise tanking).
"Air is beautiful, yet you cannot see it. It's soft, yet you cannot touch it. Air is a little like my brain." - Jean-Claude Van Damme