Issue for me would be that batteries eventually die which would render the whole derailleur useless.
From my perspective, worrying about a dead battery is a non-issue.
1. The fixed batteries on the new generation EDS derailleurs can be removed and replaced.
2. When the battery pack fails, purchase a replacement. (
As long as the derailleur/s are for sale, and perhaps for many years after production stops, a replacement battery pack will be available.)
3. For other products that I have purchased, where I could no longer get a replacement battery pack, I have carefully opened the battery pack. In in every case, the battery pack used common and readily available rechargeable battery sizes.
4. If by chance, I haven't worn out the mechanical part of the derailleur by the time I can't get a replacement battery, then I would make my own battery pack to keep the the derailleur running.