Alright, I'll start off,
First of all I'd deal with the problems of X-country mobility in deep snow. This would lead logically to wider tracks, bearing in mind the 1:8 ratio required for maneuverability (see Lance I did learn something in those AFV design classes during AGS
) Along with that, due to the stresses associated with turning in deep snow (or mud for that matter) I'd do away with center guides on the tracks and replace them with outer-guides like on some of the soviet tanks but I would make them longer to reduce the possibility of throwing a track while turning in the snow. Having eliminated the center guides we could then go to a single roadwheel design instead of the outer and inner so common now. The Outer-guides would by necessity be farther apart than center-guides and be removable to allow for the changing of roadwheels. The roadwheel would be larger than what is on a tank now, say the height of an AVGP tire. Perhaps in order to reduce weight it would not be a solid rubber tire either but a mesh like rubber design which gives the tire the qualities of an air filled tube but without the inherent problems of flats.
Current tank design doesn't leave enough clearance for deep snow, as anyone who has done a 6A or B in Gagetown in mid-winter will tell you the tank often ends up plowing through much of the snow and in some cases can be stopped dead by it. This leads me to the conclusion that the tank aught to be able to raise itself (and lower itself) for the conditions encountered. To solve this problem I would have a hydro-pneumatic suspension, but unlike the hydro-pneumatic suspension on vehicles like the BMD the raising and lowering of the vehicle would not create a corresponding effect in the track (i.e. it wouldn't become slack). This means that the tracks & suspension would have to be almost a separate section from the rest of the vehicle, a fixed unit.
This offers some tactical advantages as well as the practical advantage of increased clearance in that it could allow a vehicle to pop up into a hull down from a turret down in order to engage targets. For that matter if there was no superstructure of the hull above the tracks it could even allow the vehicle to be laid on it's belly to make for a smaller/harder to Identify target when in a Hide.
The basic hull of the vehicle could conform to standard tank design, though it may be narrower due to the increased width of the tracks, this causes some problems with regards to armament, reduced width means reduced turret ring size. Common wisdom would tell us that in order to be effective against modern threats the armament should be in the 120mm range or pack the equivalent punch. Along with this is the whole question of weight, still a factor when dealing with a snow covered landscape or thick mud from spring thaw so instead of a conventional gun would missiles be more effective?. Due to cost I would opt for LOSAT over fire and forget type missiles and mount them in a turret. Question? Is there a rocket which relies on KE penetration, out there that is small enough/effective enough to fit the bill?
Just some thoughts.