Lets not forget that there's stylus and then there's a proper stylus, and proper active stylus needs hardware. There's no indication that there will be active stylus support by wacom or similar.
I mean Microsoft didn't even manage to get wacom onboard of any Windows 8 RT tablet, so certainly don't hold your breath on Windows Phone any time soon.
And if not - what's the point of this device?
Plenty. I can't actually find any reason why I would ever use a stylus on a phone. I do use wacom stylus on my Windows 8 tablet daily, partly because of my studies. Last thing I would want is to stare my phone anymore I do already and use stylus to distract me from the ease of use of a compact smartphone.
To me much more important benefits of the big screen comes with the ability to do proper multitasking. Like on Galaxy Notes. Snapview would be perfect for Lumia 1520. Will Microsoft implement anything like that? Probably not. They are still figuring out how to add notification center after all.