The D-Bus spec generated RequestableChannelClass struct is spreading across TpQt4 APIs at an alarming rate (:D). While we already have some higher-level accessors such as ContactCapabilities::supportsMediaCalls(), should we, in fact, have a higher-level ChannelClass object (similarly to Channel::GroupMemberChangeDetails) wrapping the variant map and having accessors to the well-known channel immutable keys (such as {set,has,}ChannelType), etc. There should also be something to manipulate the optional parameters array with.

I believe this would be most useful for the planned filtering API additions (bug #29090), specifically constructing filter channel classes and making sense of existing filters. It would also provide a middle ground between the CapabilitiesBase::supports() accessors and the bare variant map access still needed for some tasks (at least in extensions).