The picture in the op seems to be misleading, 1.12.2 is not available in the badlion client, someone posted this on discord yesterday. I personally can't try this since there it also doesn't support Linux (or any OS other than windows).
https://cdn.discordapp.com/attachments/310059423966035968/452362805027536896/Capture.PNG
We all know that the definition of "soon" can be somewhat flexible at times. It would be infeasible to make the badlion client mandatory at this point.
Many people here seem to have a lot of confidence in it, I don't believe they will be able to maintain a completely secure system, even only on Windows. If the client becomes popular, there will be exploits, probably fewer than without it and they might be fixed quickly, but you won't be able to blindly trust that a badlion client user is not cheating.
If it is not mandatory, I don't see how it will reduce the amount of cheaters at all. Those that don't have a bypass for the badlion client will just not use it. You can require it for private tournaments if you want to exclude Linux/Mac users, but I don't think the server should be involved in that at all.