That type of controlled opennes only exists with Android, Qtopia kind of has it also but in a sucky way and Archos has already tried to go that path and it wasn't cool enough.
I'm not sure about Qtopia. So far as I know -- and I've been developing for Qtopia for ten years -- Qtopia is supplied either as a fully open or fully closed platform. There really isn't a way for a vendor to provide Qtopia with _limited_ ability to run code. Qtopia apps are, by definition, native C++ apps, with all that implies. A sandbox for C++ apps could be contrived with a bit of effort but, so far as I know, nothing like this has ever been implemented for Qtopia.
In my view, the simplest way to open up the Archos units for development would be to provide a decent Java virtual machine, the privileges of which can be controlled through a Java security manager. Unlike C++ (and Qtopia) Java was designed from the very start to work this way. This is, after all, what Android is doing, and it's what the mobile phone vendors do.
The tricky part, as always, will be to give Java apps enough rights to be genuinely useful (which means as a minimum they need to be able read/write local files _somewhere_, and manage network connections to arbitrary hosts), while not compromising the security of the host unit. I know how to do this, but that's because I work in the Java business, and I've spent years dealing with issues like this. I imagine Archos could
do it if they wished, but it may well not be cost-effective.