Nokia has not announced any additional Maemo 5 devices.

Nokia has also not announced that there will be no additional Maemo 5 devices.

There's an expectation within the community that eventually the Maemo product line will expand out to include more than one device at a time. There's been no official word from Nokia on the matter though, and any discussion on a second Maemo 5 device, or multiple Maemo 6 devices, is speculation at this point.