For what it's worth that's two seconds between when one signal was unexpectedly cut, detected, shifted to the other, windows scaled up for a mulimedia stream and the app buffered enough to decide to start playing audio again.
Something considered a two second handoff is going to result in a far longer stream interruption than that in any method I've seen used especially considering the app is not assisting with the process or getting state transition info which it could be if built with mptctp aware libs.
I'm not saying multipath TCP will be very nice for mobiles, but it will mostly be home and work networks that will be used, just like how it is for wifi use in the mobiles today.
As for 2 second handoff being smoother than anything else out there today, that is just not true. The situation for phones doing handoff with EAP-SIM/AKA is pretty similar if not better.