On the one hand it would help filterset authors. But on the other hand it makes filterlist creation/filter possibilities much more complex.
This is a good thing. It makes ABP more powerful and allows for shorter rules to be more precise.
Already today creating filters is not easy, because many people does not use wildcards.
Creating a good filter list beyond a simple wildcard-less URL list never was easy in the first place.
Seeing similarities in different URLs and using them to make use of wildcards can be tricky and needs some experience.
But when this would be introduced, this would become a complete overkill; even skilled users will be confused.
Nobody forces you to use new syntax capabilities. This is an extension to existing syntax, so everything will stay valid.
Make a new column, where such options can be saved. Generally it would be clear or set to "always". But the user can edit this aditional field and set a limitation (e.g. "image" or "image,object")
Like a permission mask - that's actually not too bad an idea.
But I'm not sure if a field of checkboxes allowing for negation etc. for every available selector would be much easier. I also see a problem in reflecting a filter line's mode in its row without making the row too large. Additionally, there is still need for a representation in plain text for exported lists, so why not file this syntax in the same "advanced and experienced users only"-corner as ABP's ##-capabilities? I'm sure they can be confusing as hell too...