How do I add this as a suggestion .. do i create an issue on the authoring tool github?

No, on the framework for this particular one https://github.com/adaptlearning/adapt_framework/issues/new

I've been making lots of use of the humble text component for where I need an overarching intro and instruction on a block slider underneath

Ah OK yes I completely see what you mean. I think you could also use the article body and instruction to get the same effect... or you could if the article's instruction property was exposed via the authoring tool like it should be. I'll see about getting that fixed!!