Getting a standards-compliant XML parser into 2K lines is going to be a challenge, if you're not going to cheat on what a "line" is. You must be able to deal with both UTF-8 and UTF-16 [1] (and remember UTF-16 can be in either endian order), you have several tables of things like what chars are valid where, you've got data structures to declare, and there's a lot of edge cases that may not leap to mind but if you don't cover them you don't really have an XML parser, like CDATA handling, entity loading from a DTD, parsing DTDs at least well enough to get those entities, processor commands, etc. A useful subset certainly, something I'd actually call a real XML parser, I'm skeptical. Not quite ready to write the idea off, but skeptical. (It's saved from me writing if off entirely because if I read the spec correctly a parser is not required to resolve external DTD references, if it was it would be stick-a-fork-in-it done, you'd eat hundreds of lines just using raw sockets to do HTTP requests and manage them even halfway properly.)
A JSON parser? Heck yes, even with the UTF-8 handling. It wouldn't even necessarily suck.