Former Flash/AS Designer/Front-end Dev here with a couple of thoughts; Timeline animation is the most obvious feature of Flash to most people, and it was also the reason why so many Devs hated Flash. This niche is for Animators, and there are lots of timeline animation tools around, including Animate, which is just Flash rebranded. I used to teach Flash as well, and 'easy to create animation' is a relative term for sure!

For me, the value in Flash was the Stage, Symbols, and the Library, using the single frame movie paradigm. This allowed designers to import graphics and create complex UI layouts, interactive content and animations using Symbols, which could then be controlled using Actionscript.

In that light, I think a good path would be to create a Flash-like visual IDE that integrates with Haxe, which has a ton of target languages and platforms, but which lacks this kind of visual front end.