You could recreate famous battletech battles where each side would have a fixed dropdeck of stock mechs that are balanced for each team and any player that queues in will drop in a random stock mech on a random team. (With no need to purchase mechs since this mode is standalone)
An example would be something like the Battle of Luthien where you would have like 12 stock lore-correct IS Kurita faction mechs fighting type 8 stock Clan Smoke Jag mechs on River city conquest.
You could have event prizes going on for individual achievements similar to the ones that PGI has already been doing and run it for one week out of the month.
This would be fun for everyone in the playerbase from noobs, to battletech lore nerds and the hardcore competitive guys and it would be a fun break from the solo queue grind or CW.
EDIT: This is not the same thing as "stock mech mode" which would be a balance nightmare considering that most stock mechs are terribly bad. PGI could playtest and balance the loadouts for each team to make sure each side has a even chance of winning.
Edited by Panzerkampfwagen IV, 21 January 2016 - 03:57 PM.