in regards to the character roster, Pre sequel(that is needlesly hated so much for being a BL2.5 which is actually a good thing, sinc ethat means that Borderlands 2 is not a thing you can copy easily) teased a Vault Hunter roster because “you need all the Vault Hunters you can get” as a reason.
meaning core unlocked Vault hunters and unlockable ones from Recruitment missions. That also means that something like Cyborg resurrection of Roland can happen.
for the loot gain, an Arena where you get loot including special loot would be good. Grinder returning for “leveling up” your gear’s rarity would be good as well as a weapons work bench that increases the level of a weapon by changing the low level parts with the higher level parts.
Plus a Borderlands 1 style loot system would be better. And the weapon proficiency feature could return.
for the Arena, a reward could be Gearbox Manufacturing weapons that include Borderlands 1 aesthetic weapons and cross promotion weapons and items as well as rewarding you will skill points like in Moxxi’s Underdome.
in regards to the microtransactions and lootboxes, it would probably be minimal like in Battleborn and even include golden Keys as drops from doing some challenges like how you can EARN THE PREMIUM CURRENCY from DAILY QUESTS in Battleborn.
Presequel was not a disappointment if you thought of it as a side game, meaning as a game that ties events together, Presequel serves it’s purpose.
as for Battleborn, it needs more players on PC, which can be done with Community events like Weekend Warriors and coaching and Story mode party ups.
Good gearbox games need to be supported and Borderladnds as well as underrated Battleborn are those good games.