A couple thoughts. You would lose a lot of people if it was only a once a year thing. That would lead to significant skill fade. I don't really know if some people understand how active the reserves actually are. There may be very small minimal requirements for parading, but you have to remember that that is not what the majority of members do.
I like to joke that my recruiter lied to me when he told me that it was a part time job. Yes there are the one night a week and one weekend a month, but I like to call it at least one night a week and at least one night a month. I don't know how it works in other brigades, but we also support a significant amount of Battle School courses. You had in the general extra Class A work that is required to actually run the unit, the random 10 day exercises and other training activities that come up, it's not uncommon to have members doing 80+-120+ Class A days a year.
Very true about some members doing that much time. Most I would argue don't.
This still wouldn't replace the opportunities for Class B or Class C work. I just envision a Reg Force (or Class B) member sending taskings via email to members and them stating what is available. Members could still send up whoever there decentralized contact is that they are looking for work. You can still request to go on courses to advance your career. There just might not be many of the one or two day small party tasks which exist currently as those armouries and geographical units wouldn't exist, but the larger ones still likely would. Your career would be very individual orientated and controlled.
A lot of that general Class A work wouldn't be needed as the units would stand down each year after the 'exercise'. We create a lot of the requirements for that smaller party work, because we exist as so many different units in so many different areas. A lot of the admin we have would disappear as much of it is created by the focus on Class A work and short term parading. There still could be the occasional Class A tasking, but most of it would likely be Class B for a short term contract.
I would also argue that 80+ days of Class A isn't exactly 80 days of valuable training. How much of it is simply keeping the lights on, planning exercises, sweeping the floors, cleaning the trucks, struggling to find funding, etc. How much of it is practicing your trade, honing skills, and field exercises?
The biggest benefit the 1 month training exercise would have is the fact we would have full strength units operating in the field as a army. Less focus on getting the section skills down pat, more focus on making us a effective force.
I see this style of system slowly leading to a 200k Reserve Army which could be practical. I cannot see our current system effectively sustaining anywhere near that.