IMO, any cash-for-clunkers program in MWLL would need to have some discount factor for your sell-backs (base discount eg. 50% of mech cost + reductions for destroyed/damaged parts). This feature is not intended to allow you to never spend money, only help you out if your mech is obsolete and you need to upgrade anyways, or if a component is destroyed and your mech has become worthless. (well, not only, I am looking forward to, one day, running out in a BA and coming back with a salvaged mech to sell)
If there is no base discount, I can see this as one potential way to get around any anti-pooling features that are implemented in the future (eg. player 1 purchased 20k mech and gives it to player 2, player 2 sells it for full cost, effectively transferring 20k which might otherwise be disallowed)