Nice idea for a plugin!
I started to write one with Widget, Shortcode and Options page but will have to take on it later on...
Meanwhile, I've published the bare bone, that is: a plugin for doing a Tweet Cycler Widget.
The CSS adjustments and the Cycle plugin configuration have to be done directly in the code, check the FAQ.
Here's an excpert of the ReadMe:
WordPress plugin for displaying a Widget with x numbers of Tweets from a specific user. Displays one tweet at a time, and rotates them using the jQuery Cycle Plugin.
Based on this WordPress Question, by Anriëtte Combrink.
Uses jQuery Cycle Plugin and jQuery Easing.
Function for grabbing the Tweets grabbed from the plugin Twitter Hash Tag Shortcode, by Bainternet.
A little touch of style in the Widget admin area from this WordPress Q&A, by Jan Fabry.