A workaround would be to convert the smart object layer with it's smart filter into a new smart object. That way the smart filter mask will transform with the image.
Often it would be very nice, if you could link the filtermask of a smart object to the smart object itself.
Michael’s work-around certainly works, but with regard to convenience and file-size implementing the OP’s request would seem preferable.
It would seem if a linked layer mask can be transformed with the smart object the filter mask could be linked as well.
I didn't mean the workaround to be vote against the request. But it does have an added benefit. When you transform a smart object with almost any smart filter the appearance of the filter changes. Blurs become more or less blurred depending on the transform. Same with sharpen. If you want the effect of the filter to appear the same after the transform you need to embed it into a new smart object.
When you transform a smart object with almost any smart filter the appearance of the filter changes.
Good point with many transformations.
It will be interesting if/how Smart Objects are improved with coming versions in any case, as so far each version since CS2 had some improvement there, if I remember correctly.