Yes pretty exciting. I can see how a good json-rpc C implementation could become very popular very quickly. Especially if coupled w/ language wrappers allowing rpc messages to be dispatched to and handled by higher level languages (which could also be used to facilitate cross-language procedure calls).
I currently am author of the Ruby JSON-RPC implementation RJR [1] (you can read about it on my blog [2]) but would totally be down to deprecate that in favour of a C implementation w/ Ruby bindings (provided its under an Apache-esque license) and would love to help out on this effort. Unfortunately I have my hands tied for the next month or so but will loop back around after that to see where things are at and possibly help out.
Thanks for getting this going!
-Mo
[1]
https://github.com/movitto/rjr[2]
http://mo.morsi.org/blog/taxonomy/term/112