If you do SCTP in user space with UDP encapsulation, most of its benefits disappear (and you have to do that - also because of Windows).
It's standard only on paper. There is only one significant user space implementation (usrsctp). It's used both by Chrome and Firefox. I don't think it has much use outside of that. And, I don't think other browsers implement data channels (which require SCTP).
Browser implementations will probably never have to interact with kernel implementations (which are not really used outside of telecoms). There is really no reason to make them talk the same protocol. It's likely better to use two different protocols tuned to those specific uses:
https://tools.ietf.org/html/draft-joseph-quic-comparison-qui...
They will probably replace SCTP with QUIC also in WebRTC: