I'm starting to rethink a lot of things here.
Given the ever increasing complexity of the things *we* want to do, we should be considering taking only the high end capabilities into the Regular Forces, including enablers.
For many enablers and even trades, we can augment Regulars with reservists on the UK 77 Brigade model. Imagine the CF cyber capability with half full time Regular personnel, with the other half hired from high end IT positions who can keep the unit updated with current trends, industry training and techniques. Similarly a medical unit might have its reserve half made up of civilian doctors, nurses, paramedics and other medical professionals. Service Battalions are also capable of using this model, hiring class A mechanics, and civilians who work in clerical, logistics and other trades as their Reservists.
For the Combat Arms, it is a bit dicier, but lets say each Brigade needs enough Regulars to man an IRU, and the R2HR and HR Brigades get fleshed out with reservists who fill the rifleman, gun number and other slots which require less training and experience. Reservists who are in the R2HR and HR Brigade get trade and career courses (and it is probably a good idea to "overstock" the R2HR Brigade to ensure that you will have enough people aboard when you cycle to HR), which provides a pool of people who go back to their units and provide the training and leadership in the Reserve world.
This should also provide enough actual troops to cary out DOMOPS if required, without the massive games of musical chairs necessary to carry out these tasks or cut and paste battle groups together for deployments. Even with the low number of troops available today (Infanteer's example of his battalion being short almost 100 men is probably not an isolated example), the battalions can concentrate their manpower for the IRU task, and "flesh out" with reservists as they move up the readiness ladder.
This also leads into another hobby horse of mine: equipment.
In order for a system like this to work, Reservists need to be familiar with the equipment they will fall into if/when they marry up with the Regular Force pars of their units/Brigades. Having a few large families of vehicles/equipment in sufficient numbers provides low unit costs for purchase, simplified logistics and seamless transitions between training and deployment. It also provides a much larger pool of equipment to raid when the Regular Force actually needs to cover contingencies, and is less likely to cripple Reserve training when that does have to happen.