Oil does heat up a lot in certain spots in the engine. A 100C+ increase over the sump temperature is not unrealistic. The oil will first heat up in the rod bearings due to friction, then get flung onto the warmer upper cylinder liner, then make contact with the even hotter ring, and get squeezed into a layer only microns thick, and then get further heated by the high friction in this area. Cold, thick oil will experience more friction heating, and will have a higher temperature rise than hot oil.
Gasoline is a mix of compounds that have different volatilities. Some of it will evaporate at room temperature. Leave a cup of gasoline outside in the sun and it will be mostly evaporated within hours.
I'd expect dilution to be higher in winter, but it might not increase as much as you might think, for a couple of reasons. First, 70+mph highway cruising is not generally the best-case for dilution. Dilution goes up a lot with higher engine load and rpm, so lower speed driving with a warm engine would be better.
Also, GDI engines are often tuned to reduce fuel dilution while the engine is cold, by increasing fuel pressure and advancing fuel injector timing. Once the oil temperature and intake air temperature are both high enough, it will switch over to favour efficiency instead of dilution. This is the way my Subaru is tuned. I'm sure it varies by manufacturer.
I was referring to fuel travelling the other direction past the rings, from the crankcase to the combustion chamber. Some of the fuel vapour will escape this way, while some will escape through the PCV system.