Hard keys basically fall into the "non-direct" approach whereas touch UI's work on more direct approach ...
There are 'good' alternative UI's for text input, Shapewriter etc ...
I'd say that it's good to plan and design so that you can create a Maemo device that works without _requiring_ the existance of a HW keyboard, but that you can also create devices that can have the HW keyboard and can therefore provide better text input with it. [...] Support but don't require.
Therefore you can have a "productivity focused device" with a HW keyboard and say a media-consumption device that skips a keyboard for smaller size and/or other features. (These are of course hypothetical device examples.)