Speaking of the GUI...
but it will, for example, allow users of the GUI to pay any Bitcoin address with Monero from their GUI wallet using an xmr.to plugin.
WOW!

this would be a fantastic ease of use feature! Allows quick and easy inclusion of all existing bitcoin accepting vendors. Very cool! I'm getting more excited every day!
Any particular reason why is the upcoming GUI integrated with XMR.to and not Shapeshift?
There seems to be differences between xmr.to and shapeshift which is significant enough for XMR developers to use the former...
probably because it was easier and quicker for now, but i'm only guessing. Maybe smooth or someone can chime in.