On variants:
The problematic and interesting thing is, that on one hand it's pretty difficult to add variants to some mechs, while on the other the new weapons allow variants that go far beyond 3025. For example: we've one Enforcer in the game, the 4R, which comes with an AC/10, a LL, and an SL. There are no variants before 3025, at least none that I know of. However - the 5D model introduced in 3050 swaps the AC/10 and the LL for an LBX-10 and ER LL plus an additional JJ - perfectly doable with what is in the game right now.
I'm very undogmatic when it comes to "lore" and "canon" - I tend to focus on the game and fun, if it's not too much of a stretch. With the inflow of future goodies being part of the game, future Mech variants would be possible as well, as shown above. The thing is, that THE PLAYERS can build a 5D just fine, if they want to, and I'd be more interested in upgrading the AI option than in backdowngrading the players here.
I could imagine that others see this different, though-
5th Jump Jet likely requires an XL engine and possibly other goodies to get up to 5/8 speed with the same payload. Slapping an LB-X and ER Large Laser on the 4R Enforcer does not result in a 5D.
Right now the level 2 construction tech drawbacks such as reduced critical slots and engine side torso destruction are ignored since there are only a few lostech mechs (Atlas II, Highlander 732B, Black Knight 6B, Griffin “2N”, Bull Shark).
Adding a bunch of level II tech mechs is a colossal balance landmine, I would be shocked if that happened.
There are some low-hanging fruit that don’t even need a separate chassisdef, just a mechdef:
Jenner -7F
SRM/JJ Trebuchet (on second thought may have an extra medium laser)
PPC Grasshopper (technically out of timeline, but basically a mod that happens when the mech’s large laser gets destroyed and there is no replacement laser available but there is a spare PPC lying around)
2 LRM 20 Stalker
Adding these as separate chassisdef would unnecessarily complicate the salvage pool IMO.
Slightly less low-hanging fruit (can be done with current chassis if you don’t care about weapon placement):
Wolverine 5M (use 5K, extra medium laser in the wrong arm)
Several Marauder variants
Hardpoint configuration exists on MWO model and no variants in game (will almost certainly be in 1.9):
Grand Dragon
PPC Zeus
Marauder variant
Problem children: (no level 1 tech variants IIRC)
Enforcer
King Crab
Firestarter? (Suggestion: “walking warcrime” inferno missile variant)
We don’t have one and it’s kind of weird:
Hunchback with missile hardpoints. (Speed 4 medium “stock” missile boat for the opfor, players can already use the Centurion)