Only being able to make 1 item at a time in the workshop means the chance to get epics is not as good as it should be. My suggestion:
Add Workshop Warehouse. Have it take up 1 spot in hideout. Add 2 of them to the game. It will make modifications based on the level of the players workshop. It will only present 1 option of what to make.
Make it upgrade the same way Brokerage does by low resource cost but high time for placement and upgrading.
Level 1 Workshop Warehouse has 10% reduction of common modifications appearing as option.
Level 10 Workshop Warehouse has 100% reduction of common modifications appearing as option.
Benefit would be to allow for Herocon based on making of modifications and 3 chances to get epics per 12 hours instead of just 1 chance.