Ok, let me reply to my own question I asked a year ago

In short: it's possible to go to Gilgit year-round for sure and the weather is even very pleasant actually (if it's not raining)!

I went two weeks ago (beginning of January) and it was pissing rain for 15 days non-stop. You can ride, it's not too cold, but you won't be able to enjoy the views a lot if it's raining. 3 days after I left Islamabad the rain stopped fortunately, the skies were completely clear and it was nice and sunny. I'd say around 20 degrees celcius during the day in the sun! Excellent! (I only reached Dassu and had to turn back because time was running out, after Dassu it may be slightly colder, but don't worry).

But here's the problem: during and after the rain, the rocks start falling! This completely blocks the road in several places and can take up to one or two days to clear. This is what they mean by 'keeping the road open': it's not about snow, it's about rocks!

People told me that it IS possible to get stuck if you go beyond Gilgit, i.e. you go to Karimabad or Sost, snow falls, and you're stuck there for two months. It happened to a Japanese guy apparently.

If you want to go to the border, be prepared: people I met there said it was -25 celcius at the border! But that's at more than 4700 meters I think, Gilgit is only at 1500 meters and the KKH up to Dassu is at most 500 meters or so I guess, apart from a small pass just before Battgram.

Oh, and you can forget about going to Swat, Skardu or any other place off the KKH. Even in Murree there can be a layer of snow of more than a meter. They keep the road open, but it's very cold up in Murree. So go via Taxila/Hassanabdal/Haripur/Abbottabad to Gilgit.

cheers,
Peter