[Suggestions]
If the Team Death Match mode continues as is and the 'MechLab is added, here are some suggestions:
1) 'Mechs are to be configured outside of the game (if Crysis allows this, but probably not).
Reasoning: So you can configure mechs for hours of fun. I enjoy this.
2) You will be able to choose one mech (or a specific number of mechs) per weight class/vehicle class that you can bring into a game.
Classes could be: Light, Medium, Heavy, Assault, VTOL, Aerotech, etc.
Reasoning: To make the default variants still viable if the situation in-game makes your custom mech not as effective (tactical reasons).
3) Cost of the mech would be calculated by what you have on the mech.
Reasoning: To fit into the Rank-up c-bill scheme so custom mechs can be balanced. Then you can even factor in if you have a 7 ERLL NovaCat, you can make it more expensive thereby nerfing it. If people use a particular loadout most frequently and it seems "cheap" or "overpowered", it can be nerfed by making such a loadout more expensive in the next patch.
Example) 1 ERLL costs 4000 cbills, then adding the 2nd ERLL will make that one cost 4100, and so on until the 7th one will cost 6000cbills.
[Advantages]
Advantages of these three features would be:
A) They can be applied to other game modes easily making the "Rank Up system" viable in all game modes.
B) You can't change custom loadouts on the fly, making preset variants more viable and "worth it".
C) Only having a limited amount of custom mechs at a player's disposal per class ensures that their custom mech will not always be a viable class for a given tactical situation.
[For example] if the custom mech is well suited for long-range battle, but does not have defenses against fast and light mechs flanking them, and the opposing team has chosen to use many fast and light mechs; It would be advantageous that the next mech the player buys is something else that is better against fast and light mechs.
D) Balancing custom designs can be done by just tweaking costs of certain loadouts/items/multiples of items.