Before getting to the meat of my thoughts, I'd like to point out that I recognize 2 things: 1. I have searched and I am aware of the previous discussion and "No" consensus stated by a dev regarding persistence. 2. This mod is its own game (and a very good one at that) and is not trying to be other games or their direct competitors.
That out of the way, my reflection and observations are based on the simple truths that MWLL is fun for a while but doesn't always keep the interest of players (incuding myself) long-term and that the player base of this fantastic mod is MUCH lower than it should be. The mod (game) should be the worthy successor of such wildly popular free mods such as Counter-Strike or Red Orchestra but instead, IMHO, has fallen prey to gamers who have been "spoiled" by the revolution of persistence. And with persistence, hand-in-hand goes risk/reward of 1-death-per-match (reluctance to die rather than quick respawn).
What seemed like a gimmick when Call of Duty: Modern Warfare and whatever other games really perfected the implementation, became one of the greatest revolutions to gamers - credit for time played. Who wants to start over every time they re-start a game or map? As much as our intellect tells us it is just cheese, our inner boy/girl can't help but giggle with glee (on the inside, of course) every time we unlock some new toy or ability. Case in point, World of Tanks is not half the game that MWLL is visually, mechaniclly, or feature-wise... but its playerbase is astoundingly larger. My explanation/theory is simply: persistence and reward.
Long post summarized: Implement 1 mode only that utilizes some form of persistent reward in a 1-death-per-round/objective capture mode to gauge its popularity. If it doesn't work, the mode can be changed or even trashed and you say we tried to find the golden egg but came up short. If it does work....
The sort of persistence I would suggest is rank - which equates to starting money per round. Buying each chasis ala World of Tanks probably would cut down on diversity and be a bit unruly given the number of choices. Rank points (for lack of a better name at this point) would be earned for damage done rather than just kills and would be multiplied for damaging/killing larger mechs and higher ranked players such that newer players gain a bit faster at start and tends to lean toward equalizing players rather than "rich get richer" models. Naturally, the winners of the round (all vehicles destroyed or objective accomplished) get a 50% bonus to points.
In addition to feeling like the player is rewarded for play-time, different classes and roles for mechs/vehicles will have a more consistent place in battles such that it isn't all lights to start, then mostly heavies near end of a 40 minute match. win-win for those who love lights/mediums and for those who enjoy more diverse tactical features.
Example: I join a battle as a Lance Captain (I forget acual names, bear with me) and have 62,500 credits to buy my mech/ammo - I start in a medium. My teammate joins as a Star Colonel and has 84,000 - he starts in a heavy. Teams are balanced by ranks.
Call me crazy or say I "don't get this mod" if you'd like, but I just wanted to offer my thoughts. As this is more a philosophical discussion than feature suggestion, I posted in this forum rather than "Suggestions". I'm a big boy, criticize away!