Imho, the vivaldi route is a good one. Taking an existing and proven device that is affordable, hackable/open source-able (for some value thereof) and resellable, and then putting a proper linux on it and selling it is a very good proof of concept and i hope that it even is a minor commercial success. I just hope that they really can get the touchscreen code out in the open so that they correct Zenithink's horrible GPL violation.
Hashing out working "roms" for __all__ the various tablets is a sisyphean task, especially since most vendors are gross GPL violators. Better to get a few actual results in the real world than just make bold statements and raise expectations that cannot be met.

