it supports?- yesStandard Socks5 does support UDP since its beginning -- RFC1928 , March 1996.
it is implemented on majority proxy selling services?- no and rarely ever
whether we will see UDP implementation on commercial proxies? very likely soon
Every other socks5 client that routes sock5 via TUN/TAP(VPN) mode support UDP- Socks5 clients that don't support it and don't plan adding support of it.
Only proxy routing clients on system level like Proxifier dont support it