My regular day to day workflow involves cutting and delivering 4K XAVC-S 100mbit footage from the Sony A7S II. I've done it on my Late 2013 in Premiere for quite awhile and its not perfect but very, very doable as long as you're light on clip effects and apply LUTs/color later in the process.
My first day with the 2.9ghz/Pro 460 equipped Touch Bar MBP gave me noticeably better timeline performance in Premiere, but exports aren't much faster. FCPX preliminarily is showing me some pretty blazing fast speeds taking clips in and encoding them as a test, but I need some more time with it.
I wouldn't try doing this on a 13". The dual-core CPU and lack of GPU grunt is going to show big time.