Panasonic has announced a big firmware update today.
It's especially good news for S1 owners.
Also - BRAW / anamorphic goodies coming for S1H shooters (via HDMI).
New blog post:
https://www.eoshd.com/news/firmware-update-turns-panasonic-s1-into-an-s1h-with-record-time-limit-in-demanding-modes-like-6k/
I understand your concern but, I haven't had a single trouble going with external SSD storage for years now. I simply don't care to hear about for anything other to be honest : )
With the right rig, no need for worries. Really :- )