Hi!
I am not aware of any current plans to automatically set your 3CX Extension Status when you join a 3CX WebMeeting.
Technically speaking, joining a meeting does not "block" you from receiving calls, and because you would be joining a meeting using a Web Browser, very likely from the same browser you have your WebClient open in, or the same PC that you have your Desktop App installed on, you can easily with 2 clicks change your status.
Also there are some challenges, when you are the scheduler of the meeting, OK, but when you are simply invited by someone else, it opens in the browser, your extension is completely unaware that a meeting is going on.