Are there (ideas for) GNSS based attitude indicators? With upcoming GNSS systems that have better accuracy than GPS, could there be an GNSS based attitude indicator? Does maybe one already exist?

I could imagine having 4 sensors (front, aft, left wingtip, right wingtip) that then calculate the attitude.
I suppose you could but what benefit wound a GNSS based system offer over traditional gyroscopic and AHARS based attitudes systems while offering better redundancy against a system reliant on outside radio sources and risks with system outages, etc?