Most excellent tool. Thank you.
To make it really git-friendly you could add the ability to export the blueprints as JSON strings.
With the strings in JSON diff routines can actually compare the changes rather than merely recording the blobs.
To improve the human readability you could make it pretty printed JSON.
If done, it should be an option. JSON, even minified, is going to take around 4x the file space, and pretty printed will nearly double that.
Of course, the JSON string may not be available to the mod unless the user has turned on that option in the hidden settings 'allow-blueprint-export-to-json'.
Another advantage for JSON, especially pretty printed, is that not only can it be diff-ed, it can be hand edited to make improvements, or even variations of the print for later use.
While pretty printed has the advantage of being easy for humans to read, in Linux (I cannot test in Win/Mac) the pretty printed file cannot be imported by drag/drop, and in Linux the pretty printed string cannot be imported by drag/drop. (Win/Mac cannot import any string by drag/drop).
[Bug reports filed on both Linux issues, but it's not looking promising.]
My Perl script makes fast work of the conversion already, but others may benefit from the option.
Still, a great, and sorely missing, tool for big print users. Thanks!
Speedrunners should be singing your praise on high.

I was thinking about JSON, but it needlessly complicates things. It introduces an extra conversion layer on import. The whole point of the mod was to quickly export blueprints that are ready to import in-game.

Works just fine for me. The file size for a JSON is no joke. I only mentioned it since you'd brought up git in the description.
All mine are stored in JSON, but I've got the Perl script to handle it solo or in batches, so it makes no difference in my workflow.
Still. having the ability to just dump the whole library is excellent. Great tool and already on my permanent list of tools for designing with.