I'll jump in first, please.
When it comes to actually trying to develop niche capabilities in the reserve force, various historical studies have found varying rates of success. Initially, reserve units have been tasked with things like laundry and bath units in support of the regular force, and found atrocious retention rates, whereas conventional infantry units continue to attract and retain reserve recruits. You have to tread very carefully with the idea of creating specialty niche units within the reserves, where again participation is voluntary or at least currently voluntary.
The demands that are placed on primary reserve members are so wide and vary so greatly. Instead of actually trying to develop niche capabilities, which rely again on volunteers who may or may not determine they're going to provide their service or not, my recommendation is that we actually look at broadening the terms of service for the reserves, so that they can be called upon when needed, but that they come with a wide and broad variety of skills.
Additionally, creating domestic response reserve units would mean that they have specialized skills and training, and they would not be able to deploy internationally, when called upon, as well. You want to maintain a broad pool of reservists, and you want to be able to call on those broad pools of reservists decisively when crisis happens.