> I can’t tell from my very quick look so far - did anyone ever make dynamic plots?

I have that in muO. Download the muO image at 
http://www.zogotounga.net/comp/squeak/muo/muO290.zip then in the image 
do a right-click on the world, from the menu that appears select "live 
documentation -> examples -> basic -> Function editor example 2" and see 
what happens.

Stef