The primary use case that this bug precludes is one in which the container.js script (and subsequently rpc.js) are loaded in a separate frame than the main content page, i.e., the page that contains the gadget iframes.
The use case above will break outright because rpc.js makes the assumption that the ScriptFrame and ContentFrame are one and the same. For instance, in rpc.js, setupChildIframe() uses document.getElementById() which fails because that script is being executed in a ScriptFrame instead of ContentFrame where the iframe resides.
One solution would be to enable the rpc.js to load in a separate frame by introducing a "context" object that can be set. This would be similar to what dojo.setContext accomplishes. However, this solution would still require some prototyping to see if it's feasible.