Anything related to RTCRtpSendParameters (previously RTCRtpEncodingParameters) really.
For example, RTCRtpSender.getParameters is missing and the setParameters seems to be missing (unless that's the send function). And as far as I can tell, you are not supposed to call setParameters without getParameters first, so that's not spec compliant ;)
And of course, the sendEncodings property of the init parameters in addTransceiver is missing. It is required to setup simulcast (and later SVC when we standardize it).
Also, my take on this is that you should probably not mix WebRTC and ORTC APIs. Those are quite different (even if there are similarities).
If you want to implement ORTC, fine, but you should probably do it in another package and make sure you don't expose fields in WebRTC that aren't part of the standard. Some fields (like the SSRC field) is not exposed for good reasons.
For example, RTCRtpSender.getParameters is missing and the setParameters seems to be missing (unless that's the send function). And as far as I can tell, you are not supposed to call setParameters without getParameters first, so that's not spec compliant ;)
And of course, the sendEncodings property of the init parameters in addTransceiver is missing. It is required to setup simulcast (and later SVC when we standardize it).