Some types like mw:ExpandedAttrs are universal, meaning they can apply to any element and their presence shouldn't be taken into account when figuring out which node handler to invoke. The node handlers themselves probably do need to make decisions based on their presence, but that's fine, they can do that already.
For now the approach I'm considering is to add the concept of a universal RDFa type, which will be ignored by ve.dm.ModelRegistry#matchElement for all purposes (including the "if not all mw: types are matched it's not a match" logic and all of that). mw:ExpandedAttrs and mw:Error (the latter would be introduced by bug 50788) would be universal types. mw:Placeholder wouldn't be one, because it needs to trigger alienation.