My 2c. I was thinking about it as well. IP phones (MiNET) don't have any configuration. They just download software image. 53xx phones just check for updates and don't download anything. The only configuration availble from external source is IP address of ICP in DHCP options. MiNET phone will not work in stand alone mode, it must communicate to the controller, because all actions like button pushes and handset lifting are sent to the controller and controller will respond with commands what to do like make a beep, display a string, open voice channel and etc.
Complications with SIP configurations is that you have to replicate those configs across your network if you have more then one ICP because DHCP will always point to the local ICP as TFPS server.
You can maintain your own TFTP server(s), but it makes things even more complicated while you will have to maintain the same version on all ICP controllers which is recommended, but not always possible. Plus if you don't have TFTP server on site, then in case of WAN outage phones may become not functional.