I should add that this is to fix the bug that subscriber notifications don’t show up for previous TWITCHCLIENT versions (< 3 and IRC clients). That will be fixed. I cannot say whether we will support JOIN/PARTS for newer TWITCHCLIENT versions, although I can see how that can be useful.
We’re currently in the process of re-thinking how we support and deprecate different client versions without causing headaches on the server or clients.