I am not sure if this really »should« work. At least I could not find any documentation about it in the spec.
IMO it is clear that this should work for UICommand components, because f:param is associated with the command that this component triggers. But I don't know if this should be true for input components also, because on a non-ajax JSF request this is also not supported by input components.
The set of available options that can be sent as request parameters to control client and/or server side request processing. Acceptable name/value pair options are:
execute space seperated list of client identifiers
render space seperated list of client identifiers
onevent function to callback for event
onerror function to callback for error
params object containing parameters to include in the request
The options argument is optional.
--> you are able to specify custom params here, so why shouldn't it work via the JSF tags f:param + f:ajax?
Thus IMO we should ask the expert group about the expected behavior before committing the patch. However, I think the behavior you're describing is NOT expected in JSF 2.0 and 2.1, but it might be a cool feature for JSF 2.2.
Furthermore it could support something like this:
<f:param name="param1" value="value1" />
I'll write a mail to jsr-314-open about this!