I'm considering this, coming from a maxed out 2014 15". I reasoned then my 15" weighed as much as the old 13" pros...but it is still too heavy for any bag but a backpack. The notion that the new 13" pro weighs as much as the old 13"airs appeals to me in the same way, if I can do with it what I can do with my quad core 1tb/16gb ram dgpu rmbp...
But it probably still won't match the performance in every way and will still get hot and noisy...so I think I might just get the next revision of the 12" MacBook and use it for what it was designed to be...a nice secondary ultraportable/traveling mac.