Paizo originally wanted to get rid of ability scores and just use modifiers with 2nd Edition, but they were afraid of a D&D 4th Edition schism happening and didn't make the change when they were releasing it. Now they have the perfect opportunity to make the shift without angering the playerbase.

What I have heard is that they haven't quite finished working out how the change from attributes to modifiers will be implemented, but it is something being handled with the official changes of the remaster. What they have said so far is that we will still have the ability to raise ability modifiers above 18, we just don't know how it will work yet.

If anything I think it'd be an improvement if the text just said "you can't raise an ability modifier over +4 until lv10, and over +5 until lv20." It'd free up an ability boost at levels 5 and 15 too, which would be nice for more MAD builds.