For now Makemkv in only one tool which can decrypt BD Discs protected by aacs and BD+. In Makemkv is possible to streaming movie in to the player, now only VLC can do that. And what about Smplayer? Smplayer should also play movies from Makemkv.
You can already do that.
Launch makemkvcon stream --decrypt --minlength=60 --cache=256 dev:/dev/XXX
And open URL http://localhost:51000/stream/titleY.ts from SMPlayer
(Where Y is the track number)
You want a button like “Play DVD from player” wich launch in background makemkv, read the output to select available track number and play the first one (and add other on track menu)?