It's probably been mentioned a couple times already, but if not...
I regularly run into situations where it would be very handy to be able to pass at least one additional parameter when calling a microflow from a page.
For example, I have a microflow that I want to call from several different pages (or different places on the same page) and depending on the source, it needs to be handled slightly differently. Now, I need to make an IVK microflow for each page that adds the 'source' parameter and then calls the main microflow. That's a lot of extra microflows, where actually I'd want to pass the parameter in the request.
Sorry, i apparently overlooked your idea when creating mine https://forum.mendix.com/link/ideas/1170. But you got my vote now too.