This sort of succession plan is difficult though and potentially you end up appointing someone who isn't the best candidate.
It can work if what you're trying to do is replicate exactly the systems the current HC is implementing. What happens if Kiss' desired structure and the assistants he ends up hiring aren't suited to doing that? You have him running a system that isn't his and might not suit his style.
Likewise, being an assistant coach isn't the same as being the head coach just with less of the same responsibilities. Are you taking away valuable experience being a head coach of a Super Rugby side that would be superior preparation for being the HC of the Wallabies than being the assistant coach of the Wallabies?
If you get part way through the process and decide Kiss is no longer the best person for the HC role because other people have become available you burn a lot of currency with not just Kiss but all your coaches by effectively reneging on a promise.
Personally I think the best option is to hire the best person you can at the time you need to hire them and let them assemble their assistants at that time.
Whether it's Les Kiss or someone else is really not the point I was trying to make - it could be someone from inside or outside a Super Rugby environment currently, but I think the benefit you get is stability in succession. Again it is subjective - but provided the cornerstone of that succession is continuation of team success, then I think it's reasonable to argue that promoting from within would land you with the best candidate anyway.
Definitely agree with your assessment of the risk - especially is success doesn't come - but it's not like hiring the best candidate at the time is risk free either if the 'bit' that made them the best candidate doesn't translate to success in the Wallabies environment (a la Rennie). But this is something that has worked for other teams and not something the Wallabies have ever really explored as we've bounced from one coach implosion to the next despite hiring the "best candidate".
Hiring the best person you can when you need to is obviously highly subjective, and in the past 15 years has rarely produced success for us - whereas if (and a big if) we were to continue to improve under Schmidt for the next couple of years - why wouldn't we want to continue on that trajectory with someone who has familiarity with the system, the players and direction the team has been heading.
My case study for this is (shocker) the All Blacks. They went from Henry (Ast. Hansen), to Hansen (Ast. Foster), to Foster - and say all you like about Fozzie relative to his predecessors, but what I would give for a Wallabies coach to have a 70% win record. I don't necessarily think it automatically means that the Wallabies become one dimensional for a decade, or that there is no evolution in the team either.