Having a welcome message explaining some of the rules will help a lot and stop a lot of people getting banned and mods wasting their time on handling things that people should be aware about.
As I'm sure you know (since you posted in the thread), theymos wrote a welcome message months ago (
https://bitcointalk.org/index.php?topic=5036308.0). I'm not sure why it hasn't yet been implemented. I also made the suggestion in that thread that the message should include both a link to mprep's rules thread, as well as advice to read the stickied threads on each board.
Also, I don't think the software would need to be modified to display warnings either as we already have (or did have) warnings at the top of Investor based games (I think it was there, but doesn't seem to be anymore).
The warning is still there, but you have to actually open a thread on Investor-based games to see it.