I don't know if it's just the endless gear itch or whether I actually have a good reason for considering a switch. Currently I have a Micro Four Thirds kit as well as a Leica kit, but I mostly use the Leicas.
You can get a sense of what I like to shoot from my Flickr stream: Flickriver: Photos from Amin Sabet. Mostly I just take photos of my family and places we go together.
My Leica kit is an M240, Zeiss ZM 18/4, 35mm Summilux ASPH FLE, 50mm Summilux ASPH, and 90mm Summarit. I'm flirting with the idea of selling those to get a Nikon D810, Zeiss ZF2 21/2.8, Sigma 35 ART, Sigma 50 ART, and Nikon 105/2.8 VR.
On the one hand, it's a lot more size and weight. Here's the difference with 50s mounted:
Image source: http://camerasize.com/compact/#389.276,557.399,ha,t
On the other hand, I gain autofocus. Yet even the best AF will sometimes choose an unintended target, whereas my Leica gear (all fairly well corrected and calibrated) pretty much focuses where intended. I also have an element of distrust in Sigma AF that will be hard to shake.
In terms of glass performance, I expect things to be mostly a wash. I can't find any real problem of any importance with my Leica/Zeiss lenses, and I expect the same would be true of the lenses I mentioned for the Leica. Plus I would gain image stabilization with the tele, and macro ability as well.
Neither cost nor megapixels is a major factor in this decision. The superior low light ability of the Nikon is a small bonus to me, not a major one. My M240 has a nasty habit of freezing up every once in a blue moon when I shoot too many frames in quick succession, so performance wise that would be another point in favor of the Nikon.
I know that no one can tell me whether I'd enjoy shooting more with an SLR or a RF. Thing is, I have plenty of experience with both to know that I like both processes very much.
The reason I'm asking here at GetDPI is because there was once a time when it seemed like just about everyone was shooting a Leica, Jack and Guy included, and now the number of Leica shooters is far diminished. So I'm really wanting to get some perspective from those of you who left it behind. Are you happy with the switch? Do you ever miss your Leica?