DPReview did the right thing: "L-mount (Panasonic/Sigma/Leica) Talk"
L-mount is essentially about Panasonic bodies with Panasonic and Sigma lenses. Sigma bodies, Canon EF mount lenses (which adapt well), Leica lenses too. Occasionally even a Leica body.
DPReview got the order right in "(Panasonic/Sigma/Leica)".
The Leica L-mount bodies are largely Panasonic technology, with a Leica UI, and a weird Leica-styled body.
Questions include: "What video settings for run-and-gun?"
The proportion of L-mount users who know or care what a Q2M is, or for that matter an SL2, is vanishingly small. I suspect most L-mount users' comments on the SL2 (compared to S1R) would be - at best - unflattering, to put it mildly.
On DPR there was some talk about subdividing the "L-mount (Panasonic/Sigma/Leica) Talk" forum, to make a separate lens forum, but that was silly, because the forum wasn't a high traffic forum.
DPR only has one forum to contain all 3 brands, there was never enough participation to justify a forum for each one.
One "general forum" is necessary (maybe enough) because there are many lenses from 9 brands, not only Sigma, Leica or Panasonic that need a place to be discussed.