If we get a Skylake rMBP at the March event I'm fairly sure it will be for the 13" model only, and it probably won't be a redesign I'm guessing. (Much like last years upgrade).
If that happens, the redesigned rMBP will most likely be released as a 15" model at WWDC in June. Redesigned 13" model in Q4 '16/Q1 '17.
I have to disagree and I'm going to tell you why.
When rMBP was first introduced 10 years ago, the first model was the 15'' and then three months later the 17''. Now 13'' is the new 15'' ... and 15'' the new 17'' also they don't have any problem to release new product out of WWDC (Macbook 12) that's not a statement, but a precedent worth looking at.
The rMBP 13 is newer (broadwell) so just updating it to Skylake isn't going to mean a big difference in performance numbers (they like to advertise that), as result it won't atract as many costumers as if they sold it as a new machine: Skylake + redesign (even though if they just add color options and USB-C).
Kaby Lake availability is uncertain. Also with your release scenario they'll end with 15 (the top machine) with Skylake and the 13 inch with the newer Kaby Lake. I'm not sure they really care about this, but won't be as neat has having both new design with the same architecture, and start a logical update roadmap from now on.
Releasing a redesigned 13 inch model will hype the hell out of mac fans waiting for 15 rMBP at WWDC (assuming they can't release the 15 on March too). Personal opinion: it won't have dGPU, Apple doesn't like to depend and buy from other manufactures and Iris Pro 580 seems to be very capable of surpass the actual AMD R9 M370X. So I say (wish): Both in March!
Lets wait and see