I think it would useful to put 1.12.2 in the little text under the server name, I’ve seen way too many people try to connect on 1.16.3 and they leave and just never come back because they assume its not their fault.
I used to include the server version on the motto before joining the server, but it was ignored anyway. To make matters worse, people don’t really check the server version that I provide on the server lists either, even if I put it in the title.
I like the motto the way it is now because adding a version number makes it look far less clean. I wouldn’t mind putting it in the player hover-over like I do with our websites and social media pages, but it surely isn’t going to stop people from joining on the wrong version.
The version detection system tells a player that they are on the wrong version. I would rather have a player see that they are on the wrong version and be able to switch than to not see that player at all.
Overall, there are two routes a user will take with your suggestion:
They will log in anyway, seeing that they are on the wrong version, and will switch versions or not return.
They will see the required version in the motto and if they are on the wrong version, will switch, not return, or do the former.
I’d just like to take my chances and let them connect on the wrong version. If we didn’t have a multi-version plugin at all, we wouldn’t be seeing any of these people at all, which is far worse.