This form of punishment has always been a possibility. Personally, I don't think these warnings are necessary seeing as anybody who joins a modded lobby should understand the risks they take, especially on a game with a little more security than previous titles.
Also, as per our sectional guidelines:
#2.1Content that is forbidden to be posted is as listed, but not limited to:
g. Stories about recent banning / suspensions. We cannot help you in this field, and is something you must take up with Xbox Live Support.