I've sent my idea to the Merch support but was told to post here so it gets viewed and potentially verified. I will copy/paste the original text in here:
My fiancee and I are selling our shirts via Merch for a couple months now. Just yesterday we were enabled to upload 2 new designs a day again. Very happy about that!
I uploaded 2 St. Patrick's Day shirts right away and also edited the pricing and text on some existing shirts. The St. Paddy shirts went through without a problem whilst the other shirts are still under review. This has happened before and made me wonder, if there is a way to streamline the process.
How about you set up a "flagging" system for the process that would mark e.g. if a design has been changed or not. In the example of my existing shirts it would flag the motive as "unchanged - passed review before" whilst it would highlight the price as "changed" as well as the text passages that were edited. Either via "brand name - unchanged" "bullet 1 - changed" "bullet 2 - unchanged" "description - unchanged" etc. etc.. I hope you get the idea.
Would that not help you guys focus on the parts that have been edited only instead of re-evaluating designs that have been up for months without a problem? Perhaps you are already using such a system already - in that case please excuse my lengthy mail.