No support for custom scripts yet. But the whole concept is that we're basically building a WYSIWYG editor on top of a node-based compositor on top of a visual programming language (so that's three products in one, lots of work ahead for us!). The result is that the whole thing is a programmatic data pipeline and you'll be able to write custom scripts in both node and code form, then compose them into reusable pieces and pipelines. But since we're building three products in one, we have only been able to focus on the parts that matter most to get things working. Your request hasn't yet been one of those, but worry not, that's very much a core feature.