the cart's before the horse
Once again, the question was about "reasonable competence in less than one year."
The trouble in aikido training is that people are barely competent in taking ukemi after 18 months of training. This single aspect absorbs a lot of time and attention for the student who may only train on average 3 hours per week — so in the interest of expediency (ideally), I would all but eliminate ukemi practice for the first year (with the exception of the back-fall), and concentrate entirely on movements that are basic, practical and immediately useful.
In addition, if one has only a limited amount of dojo time per week (say 3 hours), students could then take the innitiative by using the bokken training they learn and practice on their own for at least an hour a day at home or in a park.
The way most people traditionally learn at the beginning level, there's very little they can do on their own that leads to much benefit in so far as genuine self-defense.
Many schools don't even let students touch a bokken until students are shodan. It's truly a pity.
It's important to note that in the early days of aikido in Japan, most people already had some basic training in martial arts, including kendo. I don't believe that our current training methods in aikido account for the fact that 90% of new students have absolutely no previous martial-arts training. Today, we are producing black belts in aikido that still have no basic martial-arts skills. We've got the cart before the horse.
If I could train students my way for the first year, they would be far more skilled and competent than most shodan, although admittedly knowing far fewer techniques. The strength would be in the simplicity.