Here's the problem. URL stream handlers aren't, in fact, dynamic. If you did in fact add a handler from a deployment (even if you did it indirectly via a static delegate), and then redeployed that deployment, the handler would still be served by the old deployment (it would leak, causing duplicate classes to be loaded). That's why we don't support URL handlers from deployments. The only correct way to do this currently is to use a static module.
I've been working on a framework for dynamic URL handlers via deployments but it's been rather lower on the priority list. Maybe this week though I can find a minute to get what I have up on github and I'll open a community JIRA so that this feature can be contributed.