Obviously the break points are different for everyone, but they exist; the point where it's too much trouble to adopt Pathfinder at all and you just stick with 3.5 instead. If all the core races are bumped up to the equivalent of LA +1, then I have to either 1) only allow the core races, 2) disallow the core races, and flip back and forth between 3.5 and Pathfinder, or 3) fiddle with things to make them fit; your LA +1 solution being one way to do that. At some point, if I have to make houserule changes like that too often, there's no point in adopting the Pathfinder RPG at all, unless I no longer care about using large chunks of my 3.5 books anymore.
I personally am looking for no more compatability issues (less, in fact) than between 3e and 3.5. To me, this is a major strike against Pathfinder and well on the verge of telling me that I'm not going to be interested in it after all.
The good news is that, as you say, with a relatively high degree of compatability, I could probably still continue to use my 3.5 books with subsequent Pathfinder products, but still; if I'm doing that, then the whole exercise of creating the Pathfinder RPG is a waste of time.