It works pretty much exactly like this in Dark Souls and Elden Ring. People love invasions, it’s probably one of the most popular pvp modes for rpgs like this. I think it’s a perfect way to mix pvp into playing solo content in a really immersive way. It makes farming solo content more interesting if when I bump into players they could be a bandit on the road potentially trying to kill me! And the trophy of getting their ear is more than enough reward 
They don’t even need to set it up so pvp players are more likely to match to each other. It would still be cool that some players could potentially have it turned on.
It makes me think actually, if I could think of any other pvp modes Diablo could do, invasions would be really cool.
If players could turn on the ability to receive invasions and those wanting to invade could start invasions from anywhere but be matched to any location they have visited, this would actually improve invasions from how they are in Elden Ring. Currently you have to warp around the map as you can only search for invasions in the local area you are physically in.
I would love an invasion type pvp mode and world pvp in Diablo 4 and duels.
I really do feel this type of pvp would be very easy to develop but provide tons of content for pvp players with zero affect to a non pvp players game.