Something like Logic Pro's Scripter

I have recently switched back to Cubase from a couple years with Logic Pro, and I am really missing the Scripter plugin, which I got in the habit of using for very simple but important things that I can’t replicate with the Transformer midi plugin, like making custom shaped velocity curves. I would love to have an equivalent in Cubase… perhaps based on the new script engine in Halion?

Even better would be the ability to load any vst plugin which has midi in and out capability into a MIDI Insert slot (for example, ReaJS).

+1, agree!, some JS like scripting API would be definitely great for automating tasks, non-realtime midi and audio tools, realtime midi processing, custom tools, import / export data, etc…