From what I can find, the internal Wi-Fi chip on the pi 3 is a custom Broadcom BCM43438.
Is it capable of operating in AP mode?
According to this article yes you can:
You can see the full command line process of setting up the pi3 in a gist here https://gist.github.com/Lewiscowles1986/fecd4de0b45b2029c390
It does seem to have problems if the Pi3 is booted with other wlan attached on boot, so what I do is plug them in after boot (would love a solution to that problem)