If Bitcoin had a sidechain with Monero-style ring signatures (and other privacy features) and small transaction fees, would this make it digital cash for you too?

Sidechain would not be Bitcoin and why use something that convulsed when you can just use Monero on layer 1 ?
Seeing how Lightning Network is
used, we can see people prefer simplicity:
https://www.reddit.com/r/Monero/comments/1e1b1r4/monero_crushes_bitcoin_on_shopinbit/