A sidechain is just another cryptocurrency with more bloat to ensure that it enriches bitcoiners instead. At this point, bitcoiners are desperate to get anyone to use bitcoin that they are willing to completely abandon every feature of bitcoin besides the limited supply. Hmm, I wonder why?

Chaumian cash is custodial. Even so, If chaumian cash is implemented, this will almost completely destroy bitcoin's use-case as cash, because you can just use it without bitcoin (e.g. gold, USD, etc). I would argue that the only reason that bitcoin exists is because banks decided not to implement chaum's e-cash.