I have flashed to 4.2 Beta 3, as well as 4.2 Beta 2, and neither will allow my Wifi to work on GT-i9505.
It did work at the start, but I have tried a full wipe + fresh reinstall and I cannot get it to work again, on either 4.2 Beta 3, or 4.3 Beta 2.
It just wont turn on at all. Bluetooth works fine. I have tried restarting the phone, clearing dalvik etc.
There are a few others reporting similar problems now in the 4.3 development thread.