Would be interesting to have weapons, shields and body upgrades availables at fixed levels. Something like with all 3 options unlocked, at level 20 you get presented with the variations of your weapon, shield and body and pick one. At level 30 you pick between the 2 remaining choices and at 40 you pick the last.
They could be unlocked separately. For example first rank unlock: level 20 upgrade, one random gear choice is offered each run. Second rank unlock: level 20 and 30 upgrades, two random gear choices each run. Third rank unlock, level 20/30/40 upgrades and all 3 gear choices each run.
Once you picked a particular gear upgrade, the gear replacement option when leveling would replace the base type randomly available by an upgraded type. Example: you picked a shield gear upgrade at 20, now your gear replacement option always roll a random upgraded shield instead of a basic one.
I'll post a list of suggested gear upgrades for fun later, can't now with the 1000 signs limit.