@vinzv debian is imho not the ideal base for a rolling distro. every attempt that i know has failed on the long run. So I guess they are just rebasing on Buster as it includes most of the stuff they need.
Concerning the reason for the fork is mainly de-blobbing. PureOS is a FSF adorsed distro.
@vinzv Yes, there are some enthusiastic projects which still try to build a rolling distro based on debian. Concerning the ones you mentioned:
- Siduction : based on sid, facing the issues that a sid system has (broken deps etc)
- SolydXK : only in the Enthusiast’s Editions (based on testing)
- LMDE : semi rolling based on stretch
- Kali : in don't know
- antiX : stable
- Sparky: semi rolling https://sparkylinux.org/sparky-news-2019-07/
So besides Siduction there is no real Debian based rolling distro I know.
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