It looks like FSD can drive in the snow, although this is a first attempt to do so and there was a minor issue at the end. It's able to handle snowy conditions just fine, although for a completely snowed-over parking lot it struggled. At one point it drove over a curb very slowly:
HW1 was free. I know someone who had it installed in their vehicle before it was officially announced, and I got Autopilot by only paying for the tech package (which included much more than Autopilot). HW1 was never supposed to receive FSD and there is no upgrade path for it.
HW2 did allow you to buy FSD, and those who bought it when they bought the car got a free upgrade. HW3 is still supported, although its updates come at a delay over HW4. They announced that they should receive the latest V14 update in
about 6 months. Tesla has already announced when FSD is feature-complete, FSD HW3 owners would receive a free hardware retrofit if it's needed.
Furthermore, Tesla has allowed its customers many times to transfer FSD to a new vehicle if they paid for FSD when it hasn't been completed yet. This allows its customers to avoid any delays or retrofits for FSD on older hardware entirely:
https://www.tesla.com/support/fsd-transfer