I agree with the sentiment that a small reference client would be hugely helpful. I would like one that ran on Google App Engine, for instance, and as you say, a reference javascript version would be totally fabulous.
Neither of those are feasible-- both App Engine and Javascript don't allow arbitrary socket connections, and a full bitcoin client needs to maintain a persistent connection to at least one other bitcoin client to get transaction messages."Background servers capable of running for longer than 30s" is a feature on Google's roadmap, so maybe a 100% App Engine bitcoin client will be possible in the future.