I think at one time the Monticello, IL mix mode repeater was connected to echolink, and the radio they were using for the link radio was set to receive mixed mode. but I havent seen the stations call sign on the echolink list lately, so it may have been taken off the air.
Im not aware of any digital only NXDN repeater that would have streaming audio to the internet.
However, you bring up a good Idea.
I think whenever our group gets our "I-LEAD" system operational, I might tap my base radio and feed the audio into radioreference or something so people can listen.
Keep me posted if you find out of a group doing something like that!