Nellisir
Hero
It would also eliminate all interest in the game on the part of the 3PP, and leave a clear field. Clear as in empty.
If you've got 50 3pp pdfs & print books for 3.5, then you can't have been trying. I've got half that in print books on one shelf right now, and that's what's left after having gotten rid of almost all my 3e/3.5e material. I've got far, far, far more than that in pdf...and the majority of those pdfs are less than 36 pages. Of the ones that are longer, most could be broken into smaller pdfs.
A page restriction on 3pp, while otherwise leaving the OGL intact, would not kill or "empty" the 3pp field. It would empty the print market and focus what remained on adventures, which just isn't a good niche for print anymore, but the pdf publishers would remain and adapt.
And just to be clear, I think it would be a bad idea. I wouldn't like it, and I don't want it. I don't even think it's likely. But WotC is going to look for a middle ground between the OGL and the GSL.