Fantastic article, as always. A couple of things that just don't seem necessary in an environment that already has an exchange infrastructure (which is more common). Setting the EXPR and EXCH value for the Outlook providers doesn't seem to have any drawbacks and is required if a client is Windows XP. A company is more likely to upgrade if we don't require them to upgrade all of their workstations for something that really doesn't seem that big of a deal.
Also, having separate namespaces for every service wouldn't be the default for most environments that already are using only two namespaces anyway. It would require the company to reconfigure their environment and educate their users.
The point I am making is that even though there is an ideal situation, the benefits likely wouldn't outweigh the cost to a company to fit this. The benefits would actually have to add certain value such as added reliability, performance, or stability for a company that already has an existing Exchange infrastructure to consider them.