Stills can be replaced with video easily. Track matte or mask the animation of your video screens to the word you want.
Often in animation we work backward. In other words we create an animation that is the reverse of what we desire,then play it backwards.
eg: Desired animation: dust blowing to form a word.
Workflow: Apply shatter (or similar) to word to break it into pieces.
PreComp or render out, nest in comp and time reverse.