Hi Tobias,
Seeing as we work upstream as much as possible, it seems to me that the "Purism Way" to solve this problem would be to work with other interested parties upstream to find a solution that will be beneficial for all Debian desktop users
So, I've also been speaking to Tails folks very obliquely on this so there is certainly interest out there.
If it helps, at the time we were throwing around keeping stable as the ultimate base (instead of creating a new suite per-se and all the myriad of concerns that would immediately add) and essentially "just" (hah) backporting Gnome and other applications that made sense and could be justified.
Best wishes,