I have become a bit of a Marin fanboy only because I know they work well and at the moment are relatively cheap and plentiful. The two most important components I will be looking for are some cross country type forks and the rear shock.
As briefly mentioned this will be used as a basis for a skibike. You can put monster downhill forks on a skibike but unless you are planning to do a lot of acrobatics it is overkill. The skis tend to smooth out the ride in a way that wheels cannot and you really don't need more than a few inches of travel.
Weight will also be a significant factor, you have to lift the bike over turnstiles on a slick surface and carry the bike on and off chairlifts almost everywhere, so keeping the weight to around 10kg saves a huge amount of energy.
I have used Manitou Spyder elastomer shocks very succesfully, there doesn't seem to be any issues with the cold.
I found the early Fox air rear shock worked brilliantly on the East Peak and I see no reason not to fit another, assuming I can find one in pristine condition. Running it at 200psi seems to give the correct amount of sag and allows you to kick the back end out on turns predictably. Again this is a lightweight combo.
Some of the bigger French resorts can be a bit pedantic over DIY skibikes and don't allow you the same access rights as factory built bikes. For this reason I will be disguising this project to look like a "proper" skibike and not "artisinal". To this end it won't carry the Marin stickers and all the parts will be in skibiker black or polished alluminium. Even the skis may have to be disguissed.
This winter I should be doing some marketing and research work for the French skibike manufacturer Firem and will be testing their latest designs and benchmarking the results against my own humble ride.
This picture was from my last Firem sortie to L'Espace Killy in March this year.