I threw my own hat into the ring with my undergraduate thesis, in which I wanted to create an editor for Elm which took advantage of all the niceties that strongly-typed functional reactive programming affords. I also took a closer look at some of the projects mentioned here (Light Table, Lamdu, Tangible Values, Scratch/Hopscotch, Inventing on Principle etc...). You can find its (now totally obsolete) remains here: https://github.com/lachenmayer/arrowsmith

The idea was basically: you should be able to use different editing UIs for values of different types. The lowest common denominator is code as text, but you should be able to switch on different editing UIs for numbers, colours, graphics, record types etc. The second half of this video shows off some demos for all of these: https://www.youtube.com/watch?v=csRaVagvx0M

I also had some (far too) ambitious plans for stuff like type-driven drag & drop editing (mainly for function application), which I unfortunately didn't get to implement, but you can read about them in the report: https://github.com/lachenmayer/arrowsmith/blob/master/report...

By far the most intellectually stimulating work I've ever done! We're definitely not there yet, to paraphrase Alan Kay :~)