In my humble opinion, this is a perfect use of Processing.
Shameless self-promotion: I’ve written a series of Processing tutorials which could be adapted into a curriculum, available here. That coupled with Daniel Shiffman’s videos would be more than enough to fill up a semester.
See also:
- Using Processing as an entry point in an Introductory Course
- Programming languages specifically designed for beginners
- The order of subjects in beginner’s curriculum
- Order to Teach Topics in an Intro Programming Class
- Make it easier, and quicker to get to the start
- Programming language for teenagers
For an intro course I wouldn’t worry about it. Programming is not an either-or thing. Learning one language doesn’t prevent you from learning another language: quite the opposite in fact! Instead, focus on making the course engaging and interesting, which Processing is perfect for.
I love talking about this stuff, and I’d love to format my tutorials in a way that’s more usable as a curriculum, so don’t hesitate to reach out if you have other questions.