I guess I'll address this here.
5MB is tiny. 10MB is.. also tiny. Going from the size of 1 .mp3 to 2 .mp3s does not bother me as a user in the slightest.
From a programmer's perspective, yes, I wish I could pare down the size of pulling in the svnkit library. It's possible that I may do so in the future. If I'm not able to, I will lose exactly zero sleep over it. I consider this feature easily important enough to justify increasing the .jar by that much or more.
If you're curious, half of the size comes from precompiled libraries - one to allow java to run native code, one to allow java to interface with SQL databases, one to handle SSH, etc. Altogether I refute the claim, though, that mafia only uses a "fraction" of what svnkit provides - just svn update is probably capable of accessing 25-30% of the codebase alone, maybe more. It doesn't normally, sure, but people can do a lot of advanced things to their working copies and svn needs to be able to handle all of those things. I am happily already using the feature of it merging my local modifications into repo updates, for example. I think it is fantastic that I do not need to write any additional code to support this or any of the more esoteric svn features; they just work.