Plus we've rated a bunch of creatures with at-will self-only Greater Teleport, which that "truly timeless" interpretation would just be a more complicated version of if it worked like that.
And even if those abilities weren't self-only (or if sticking the party into a bag of holding works), it probably wouldn't be asterisk-worthy. Intra-planar travel is a non-issue, you'd trivialize any races against the clock, and you could escape any non-dimension-locked encounter that went badly as long as you can get everyone into one spot to join hands, and probably a few other things I don't care to think of at the moment; but high-level play usually means reaching the point of teleportation being more common anyway. That just removes the cap on how often you can do it. Game-altering perhaps, but it won't break everything.
While I'm here, the votes so far, up to 179:
+0 W, -0 all others - remetagross, Beni-Kujaku, Xanyo
+1 W, +0 VY, -0 all others - loky1109, Beni depending on precise targeting of Planar Travel
+1 W, +0 VY and Y, -0 all others - Morphic tide, Troacctid, Caelestion
Unfortunately, the targeting is not even vague. Just unmentioned. The entire text of the ability, for those who go purely by my descriptions:
Planar Travel (Su): Ectoplasmic dragons have the innate ability to pass instantly between the Material Plane and the Astral Plane as a standard action.