Quick update (< 10min). I did the upgrade as mentioned via My OSMC → Updater on my Vero4K.
Upgrade to Stretch was smoothless.
But… since i was using the @gmc nightly builds (17.8-134) for Kodi 18 Leia i ended up in an infinite loop of sad faces when OSMC tried to start Kodi.
I fixed that by following the step mentioned in [TESTING] Kodi 18 (Leia) builds for Vero 2 & 4K for Debian Stretch.
No everything works smoothly (Tvheadend, Emby, …).
Thx for all the great work!!!