Sorry, that was more of provocation to get conversation going what other 'currencies' could be used to reward players with new modules.
We already have a million and one currencies that can be earned by just playing the game. Just add some of those to the blueprint if they feel the 'time required' would be too low otherwise. This should be just a two-hour unique and fun addtional element to the unlocking. Even if they feel time is an issue, this is not the way to solve it.