To answer the question of how hard or easy it is for neurologists to get into INR, in short, it's not.
As you have probably witnessed from this jarring discussion in this thread, the paths are multiple and confusing. The most direct paths are, indeed, though radiology or neurosurgery That is not to say that it's not impossible, but it is harder to do if you are a neurologist. One of the residents in my program thought about doing INR and is now thinking of applying to neurosurgery advanced placement in order to do so. Part of the problem is that unless you go to a neuro-run interventional suite, neither rads nor NSGY have any interest in hiring you. There are exceptions such as the NSGY group that is looking for a guy to just do these endovascular procedures and will pay well - but this serves as an example of how a neuro-trained INR peeps also can have more trouble finding a job afterwards.
But if you like neuro, and like hands on, enjoy neuro for what it's most enjoyable for: localizing the lesion, thinking on your feet. It is an ability that most other clinicians just don't have.
And then if you like hands on, you can consider doing EMGs and billing for them, or interventional pain, or neurocritical care (some programs have you putting in EVDs, BOLTs, and trachs, but for certain are things like lines, chest tubes, intubating, bronchs, etc.)! So there are still other 'hand-on' options for neurologists, so don't get dissuaded just because of INR.
