I can't imagine it ever being mandatory, at least not in our lifetimes. Maybe the feature will be forced into vehicles someday, like seatbelts or the stupid auto start/stop tech, but you'll be dead and gone before they every remove the steering wheel.
I spent about 20k more than I had wanted to for a vehicle that was available now, and had Super Cruise, because it was taking forever to get our order delivered. Now that I have it, I wouldn't give it up without a very compelling reason. In fact, I've already spoken with the local Cadillac dealer about trading in for an ESV when they get Ultra Cruise. I think there's a caddy sedan that's slated for initial release, but I'd expect the ESV will follow soon after.
Bottom line, we live in a late-stage capitalistic society where companies are going to take every single penny that they can, and there isn't a strong enough middle class to effect the markets.