First of all THANK YOU because we use piwik for several years without problems.
However, it is unfortunate not to delegate access subdomains or only parts of the site per user.
I think it should be feasible by creating two sites on two functionally URL but it created a JS code insertion 2 times and 2 times more traffic for statistics between web server and piwik.
If someone has already faced the problem, thank you for your advice …
it could also be a feature suggestion.