I think the variants will open up more possibilities for each mech. Sort of like an version of MW4's hardpoint system, with different variants having different hardpoints.
A hardpoint system would be useful for a what you see if what you get mechlab, and keep mechs acting like what they are. Vaiants would naturally be different from base units, perhaps they might have more modules as well (?)
In the base game of battletech, things like engines and internal structure aren't changed very often on the battlefield, complex internal stuff like that has to be done in a factory.
So perhaps a Dragon base variant would move up to 86 KPH, carry a light autocannon, a medium missile system, and several energy weapons. A Grand Dragon Variant might be faster, have access to more tech (eg Double Heatsinks), perhaps an extra space for a command module, and a heavy energy weapon rather than the light AC.
So there would be limited customization, not a free for all. No engine changes, no internal structure changes. Some items might not be removable.
This is a guess on my part.
They've mentioned Mechlab several times in the past, so presumably that's in the game, with Variants also mentioned, I think a limited mechlab is the most likely system.
Another system might be they limit the mechlab until you've reached a certain level of skills in the game, then slowly unlock features. This is very similiar to how btech NPCs are traditionally only alowed custom variants when they're incredibly badazzed.
Edited by verybad, 03 February 2012 - 04:35 PM.