I found the "colored lettering" animation (in Entrance -> Moderate), which at least does one letter at a time, slightly better than a horizontal wipe.
As @grochmal says, svg animation would be the only way to get "brushstrokes", but this is a decent half-way point for now.
Bonus points for anyone that can figure out how to get something that looks vaguely like a "blackboard erase" effect for making the text disappear!