I probably shouldn't be answering this as I don't have the Processing experience, though would gladly attend a work shop at one of those "cultural literacy for STEM teachers" events in the planning.

I've always advocating a mix of languages and it sounds like you get that with Scratch, its own language.  I usually think of JavaScript as the other language, in conjunction with learning about the DOM.  But then I also think of J from jsoftware.com, in part because it's so exotic and different from Python, the one I teach the most.

I wouldn't see replacing Python at this point.  The fact that it's so used in everyday science and industry makes it more than ready for prime time, both as a gateway (door opening) language and as an end in itself.

My colleagues and I believe in more fusion among the STEM tracks and topics to where the lines between "mathematics" and "computer science" and "engineering" and "chemistry" and "physics" have all been blurred.  One brings all one's knowledge to bear when solving problems.  Individuals may specialize in their skills and haunt some workshops more than others, but the curriculum itself is more meandering.  Students are encouraged to wander (the liberal arts ideal).

What used to be called "vocational education" (where you use equipment, tools) has not disappeared.  3D printers are just starting to revamp that area.  CAD is a bridge, and for that you need geometry / trig.  GIS / GPS is likewise a core area where Python gets used (thinking of Esri products in particular).

Against this backdrop, I'm sure Processing has a brilliant role to play, along with other classics.

Kirby