Why not put all efforts on good integration into VS Code for example? I ask also because FlashDevelop was a poor IDE, seems like it's based off it.
I was a pretty heavy OpenFL devotee for a couple of years. It's an amazing project, although PixiJS is a very competent competitor when it comes to building HTML5 games. Pixi has a much smaller baseline footprint (~300kb unminified compared to 1300kb unminified).
Lately we've been working with Pixi with a webpack / TypeScript workflow. It's starting to feel a lot like HaXe / OpenFL again. We are winning big in terms of flexibility and good support of workflow. We are using VS Code as the IDE and we have a very smooth integration smoothly with an Angular-based asset and config management tool. The big thing we lost however is HaXe's ability to compile directly to C++. Even when we compiled to Adobe AIR, we got much better performance than something like Cordova or Ionic.
HaxeDevelop's best (IMHO) feature was that it could switch targets easily and integrated seamlessly with the Flash runtime's debugger. So you could build and debug quickly using the Flash runtime and then compile your project to native code for production.
But yeah, in a perfect world VSCode integration would be the way to go forward.
There's always been calls to "unify" the frameworks, tooling, etc., but I don't think that's a healthy environment for Haxe. Haxe exists as a way to avoid ecosystem lock-in. It's a bit antithetical if the community imposed restrictions on how to develop with Haxe.
If you want a cross-OS IDE, or something that works on mac/linux, then use vscode + vshaxe.