The mouse theory is interesting .... because omicron is more benign - one of the problems we have with covid is that because of all this modern medicine saving lots of lives (not enough though sadly) there's not a lot of evolutionary pressure to make things more benign.

But if omicron has been in a wild mammal population without vaccination or hospitals then there might be more evolutionary pressure to become more benign.

It's worth noting that some vaccines in the past have been 'live' vaccines - essentially viruses that get passed around with a sniffle or two but no more harm. This actually what we all hope omicron would be .... I can't see why we shouldn't give the virus a bit of a help along .... the right lab leak might be just what we all need