One big feature, in my opinion, which has been requested but is still missing is the ability to select hardware inputs other than one+two from an audio interface.
At present, if you select your device as the system or voice input, it will default to 1+2 and that's that.
My interface has the ability to mirror system(including daw) output to S/Pdif so if OBS had the option to record from S/Pdif a simple rca cable would make it a very streamlined and convenient way to video and commentate on sessions.
As it is I have two use two further stages of software routing to achieve the same.
It still seems far better than many alternatives, all the same, but given that there are existing routing apps which will take whatever hardware input you want, or even 'hijack' audio streams on a per-app basis, it seems they could do more.