Viable in what way? How are you making the comparison? Each of those arts has it's own set of criteria in which to judge viability of effectiveness. BJJ in a judo paradigm typically does not do as well as well as vice versa. Same with aikido and BJJ, both seem like oil and water when you compare viability and success from each others methodologies.
It is sort of like we need to develop a framework that is generally agreed upon in which to test skills and viability. A set of conditions and test in which we could agree upon.
From there, we could view the various strengths and weaknesses of how things such as baselline skills are additive. Same wtih Judo, BJJ, Aikido techniques.
Six months, one year, shodan, etc. Take your pick, Kevin. Any timeframe at all. Heck, just using the basic training methods that Mike and Rob showed in one day (er, less than one day) and some of the students at my dojo were doing far, far better at receiving a nikkyo lock than they ever have been.
Or perhaps you think that in six months to one year, average aikido students will be of equal skill as anyone with six months training in BJJ, Judo, MMA, etc.?