Coupon code to affect multiple product prices

This is not possible without customising how coupons work. I don’t think this is something we’ll pursue doing in WooCommerce core plugin, more likely to provide it as an extension, since I think it’s an edge case really.

Please raise this on our ideas board, where we keep track of new idea suggestions and extension developers look there for new ideas to build as well.

If you want someone to build this for you, I suggest you look at a service like Codeable or Tweaky and post a job there.