I see nothing to speak against that.
- Everything is already out there (look at the Zaurus apps)
- If you lug around the device already why don't make it multipurporse?
- The hardware can handle it for sure
Only one problem left, I don't know if you can get existing GPE/OPIE apps running on either one of the current available devices. But even if it is a problem that the iLiad runs a full X environment and the Sony "i-dont-know-what" as GUI, it should not be to hard to get a existing app ported or to find one that doesn't even need to be ported.