Obviously, this post doesn't apply to the version of the game when fighting in the confined spaces of a Machine Empire facility, but it would definitely be cool to see some "light" vehicles eventually introduced into the game for games taking place on an open-air tileset or tabletop.
Personally, I think Legions of Steel in the updated ruleset works best as a smaller-scale battle game that doesn't involve rank after rank of massed infantry and super-heavy vehicles like battle tanks or large transports, BUT I do like the possibilities of fielding smaller vehicles such as the original Fantasian Hex Runner or UNE Superfortress.
Speaking for myself, I'd love to see each faction have some sort of light APC, a dedicated fire support vehicle (think a light tank or similar), and either bikes/atvs or a small flying craft. I've included some examples below to get the idea of actual size and what their role would be.
^ This is sorta the size I'm thinking for a UNE light APC. It would have a crew of two (1 driver and 1 gunner) and can carry maybe 4 to 6 UNE Commandos.
^ Something like this one-person ATV could be possibly be a good support model for Recce squads.
^ And something of this size/shape could represent a grav-tank used by the Machines or other faction that uses gravitic technology. Maybe it could also double as a troop transport if the hull were larger?
^ Finally, this would be another anti-grav vehicle, thought a much smaller one-person type craft.
Anyways, those are the sort of vehicles I think would be the best types to add. Nothing would be particularly large or overpowering on the battlefield. Again, all of this would only apply in games where you don't have corridors or other enclosed spaces, and I'm thinking they would take up squares anywhere from 1X2 or 2X2 (for a bike or single-person grav speeder) to a 2X3 or 3X4 for larger vehicles.
If anyone has any other suggestions, I'd love to hear them!