The impetus for v2.0 spec support came from Terry Jones as a result of some pyjamas work he was doing. Here's the IRC chat we had:

[04:17] <terrycojones> i've been taking a look at txjsonrpc and it seems in need of a bit of love & care. i'm trying to use it with pyjamas and had to dig in a little to find out why things weren't working. anyway, i was thinking of submitting a patch, but i don't know enough to know whether i'm really doing the right thing or not.
[07:37] <oubiwann> terrycojones: hey!
[07:37] <oubiwann> terrycojones: sorry to hear you're having problems with txJSON-RPC
[07:37] <terrycojones> hi
[07:37] <oubiwann> it's being used in production at PBS.org for the tvschedules, so it's working...
[07:38] <oubiwann> what problems are you having with it?
[07:38] <terrycojones> the issue i hit was with pyjamas.
[07:38] <terrycojones> it allows you to make JSONRPC calls, but it expects a JSON object in the reply, not a JSON array.
[07:38] <oubiwann> did you get it sorted out?
[07:38] <terrycojones> yes, no problem.
[07:38] <oubiwann> oh, sweet!
[07:39] <terrycojones> also it expects a { 'result' : xxxxx } object, and that's not done.   maybe i just don't understand it all properly.
[07:41] <terrycojones> this http://json-rpc.org/wiki/specification says that you're supposed to respond with an object, with 'reply' keys etc.
[07:41] <terrycojones> and v2.0 of the spec says the same.
[07:41] <terrycojones> here's v2.0 http://groups.google.com/group/json-rpc/web/json-rpc-1-2-proposal   but i expect you've seen all this and that i'm not understanding something basic.
[07:41] <oubiwann> ah, txJSON-RPC was either written before there was a spec or it was written when v1.0 was being bounced around
[07:42] <terrycojones> ok, that's what i was wondering. there's some stuff in there (like faultMessage or something) that looks pre-spec.
[07:42] <oubiwann> yup
[07:43] <oubiwann> never seen the 2.0 proposal (til just now)
[07:43] <terrycojones> yes, faultString etc in jsonrpclib.py
[07:43] <terrycojones> anyway, it looks easy to fix, even for me :-)
[07:45] <oubiwann> I should add this to my TODO list...
[07:46] <oubiwann> terrycojones: so pyjamas expects JSON-RPC 2.0?
[07:46] <oubiwann> does it have support for 1.0?
[07:48] <terrycojones> no, but it expects a JSON object, not an array.
[07:49] <terrycojones> this:
[07:49] <terrycojones> if not isinstance(result, jsonrpclib.Fault):
[07:49] <terrycojones>     result = (result,)
[07:49] <terrycojones> results in an array being sent back. then pyjamas falls over because it tries to do a has_key(String('error')) on it.
[07:50] <oubiwann> hrm, it seems strange that pyjamas doesn't support the earlier protocol
[07:50] <terrycojones> and it's also expecting a 'result' key in there, etc.  i can put one in myself, but it seems like that should be the job of the lib.
[07:51] <terrycojones> it may do in some way, i only started looking at it last night, so i'm only able to say what it does by default.
[07:52] <terrycojones> it generates this JS, which hits the not-an-object problem:
[07:52] <terrycojones> response = JSONParser().decodeAsObject(json_str);
[07:52] <terrycojones> if (pyjslib.bool(!(response))) {
[07:52] <terrycojones> self.request.handler.onRemoteError(0, String('Server Error or Invalid Response'), (typeof self.request == 'function' && self.__is_instance__?pyjslib.getattr(self, 'request'):self.request));
[07:52] <terrycojones> }
[07:52] <terrycojones> else if (pyjslib.bool((response.has_key(String('error'))) && (response.__getitem__(String('error'))))) {
[07:52] <terrycojones> error = response.__getitem__(String('error'));
[07:52] <terrycojones> self.request.handler.onRemoteError(0, error, (typeof self.request == 'function' && self.__is_instance__?pyjslib.getattr(self, 'request'):self.request));
[07:54] <terrycojones> anyway, i don't need it fixed in any hurry, i have some stuff working and it sounds like it would break backwards compatibility (at least with PBS.org) unless we put in something to control its results.
[07:58] <oubiwann> terrycojones: yeah, I'll need to add multi-version support
[07:58] <oubiwann> (was just looking into that)
[07:59] <terrycojones> i guess there could be 3 versions: pre-1.0, 1.0, 2.0.
[07:59] <oubiwann> terrycojones: yeah, my thoughts exactly
[07:59] <terrycojones> and you get pre-1.0 by default.
[07:59] <oubiwann> yup
[08:00] <terrycojones> sounds good.[08:01] <terrycojones> i can help, of course. it's not much work.... famous last words.