I'm not an NIR but I'd hazard to guess a match for NIR is an unnecessary burden. I don't think there's enough spots or applicants to make a match worth it.
The advantages of CAST is that it's a standardized set of requirements and everyone going through (neurosurgery, neurology, radiology) should come out with a defined and similar level of competency. Some hospitals have already made it mandatory for their credentialing. The flip side for radiologists is that it guarantees a longer track. The rad CAST pathway requires 6 mo of clinicals. A non-CAST fellowship probably skips that.
The job market for interventional neurorad is complicated. INR itself isn't a big money maker but it can bring a lot of money to hospitals for stroke admissions. More and more places become stroke centers each year so the jobs are there. The pay is obviously pretty good. If you join a PP radiology group, expect to do some diagnostic rad on the side. I feel like hospital employed NIR's will become a bigger thing, cuz they can afford to subsidize an NIR service.