Thanks for pointing that out, I didn’t realize the limit changed. Previously there was no limit, but we’ll need one going forward. For jams I updated it to 20kb, hopefully that’s enough for you.
Based on my analysis, large CSS blobs are mostly embedded fonts and images.
Now that Google Fonts, hopefully it’s not required to embed fonts directly into the CSS for most hosts.
I think having a generic image upload tool for themes would be a good next step.