For example: I know the Asus rt-n56u had/has limitations with VPN pass through, would these still apply if it were being used as an AP? Connected users would be using the AP to connect to a router which does allow VPN pass through?
Router as an access point with DHCP disabled would bypass any WAN to LAN limitations, but you are also losing all of the extra features like usb NAS, usb printer share, and wireless guest/VLAN options it as a router may provide.