Obviously the definition of what a private "high net worth" client might be is vague. In 2005, two coauthors and I wrote the CFA Institute handbook on private wealth management. In there, we used definitions from an annual Merrill Lynch global survey that used three categories. Investors with $1M to $5M investible (excluding primary residence) net worth, $5M to $30M and above $30M. In terms of my firm's business, we deal with analytical issues relating to all three categories, but we have a lot of the big ticket wealth managers (Citibank Private Bank, US Trust, Bessemer, Glenmede) as clients.
The expert system technology I am referring to is something called Analytic Hierarchy Process. Its a mathematical technique used in large scale industrial decision making. There have been a dozen or so academic research studies on how to use it for investor decisions such as asset allocation and fund selection. Here is a link to a paper from 2000 by two colleagues of mine that I think does a good job explaining the concepts.
http://www.northinfo.com/documents/62.pdf
As far as I know, our firm is the only one that actually has AHP software commercially available that has been tailored to investment decisisons.
With regard to the multiperiod problem, I introduced a pretty simple short cut that I think gets us prettty far in practice. The basic idea is that in a world with no transaction costs, the "single period" Markowitz assumption is wrong but not harmful because we can costlessly revise our portfolio to new beliefs or preferences as often as we want.
When costs are substantial, the single period breaks down because the expected improvements in investor utility when I rebalance a portfolio are bassed on population statistics (because conditions don't change in a single period world), whereas in the real world we will realize the utility increase based on the sample statistics experienced only during the finite period until conditions change. Our way of addressing this is to assign a "probability of realization, conditional on time horizon" to any expected increase in investor utility. The tradeoff between utility (return adjusted for risk) and trading costs is therefore done in a much more economically rational way.
Here is a link to a presentation I gave at our seminars in Asia last year that summarizes most of this:
http://www.northinfo.com/documents/229.pdf