I think it is odd to expect suggestions for another company’s products on the forum sponsored by Sonos. I’d have to check, but it seems reasonable to me that posts like that are against the Terms and Conditions you agreed to when you chose to use this forum. 

If you’re looking for data, I’d suggest there are other forums that you could find more unbiased data. None of those forums are owned by Sonos, at least to my knowledge. 

Sonos really screwed up (worse than any earlier mess that I recall) but long term I don’t see any other system serving my needs as well, or supporting old devices for so long.

Denon Heos or WiiM depending on use cases good luck

I think it would be an admission of defeat for discussion of other systems to be banned (except where it's obvious product selling).

Otherwise, how could someone, for example, compare features which Sonos does better than others. Or someone who has Bluesound may want some comparison advice on sound quality with Sonos. 

I'd be more in favour of a blanket ban on the overused reference to fecal material which is liberally used by correspondents, rather than banning advice on system comparisons. 

If looking at Denon make sure you look at support lifetimes. I was not happy with them.

Actually a good thing to look at for any brand, once support drops or they come out with incompatible new versions your options are limited.

Sonos did about the best they could with the S1 S2 split and the various update discount options. Well aside from bricking systems for folks that updated early, before the bricking policy change.