Prepatch should be coming out within two weeks. But if the latest prepatch comes out would be Oct 6th which is very close to launch of expansion itself. I too think it it all too soon.
Currently the PTR is more "stable" than beta but the bugs that exist on the PTR and beta are numerous. Plus, the PTR features many undocumented changes that we do not know if they are mistakes or not. Mount equipment being unlocked at level 40 is a massive nerf to a feature that came with this current expansion. I will never understand why the current dev team quickly abandons features and systems so quickly without investing some time developing further.