I think there are much easier tools than Tableau for producing word clouds. I've used http://www.wordle.net/ a few times, myself.
If you really wanted to force it, you'd have to generate the word positions and sizes yourself, then abuse the custom shapes feature to supply the word images.
Having word clouds as part of the non-graph armory would be powerful. Tableau and related tools don't deal well with 'long tail' data in my view, and being able to do this natively and at scale (rather than 2 separate solutions with lots of manual work) would be very powerful.
Please talk to your sales representative to communicate your desire for this feature.