PS Touch to sync with Lightroom?
It would be kind of weird; PS Touch deals with layers and compositing much like its desktop counterpart. Lightroom is more-or-less a glorified version of Camera Raw. (I don't mean that as a negative; I really like Lightroom. It's aimed squarely at photographers.)
Not weird, just a difference in workflow.
Here's what it could look like -
1) import directly to LRM app in DNG bypassing iOS camera roll to save space.
2) cull and minor corrections (major color balance, crop).
3) then open a few specific images in PST for cleaning up background, etc.
much the same way I use LR and Photoshop CC on my desktop. With a portable Adobe solution, I'd hope for use that extends far beyond what the other app based solutions can offer - otherwise it's just an expensive alternative to Snapseed, et al.
The sync part seems the easiest to deal with by simply incorporating the same engine in PST that now exists in the new iterations of LR, syncing image edits among all devices.
Ahh, I see. Post-Lightroom, then. Makes sense.