Well I'd be happy to strike a deal with TGC but in all honesty I don't do this for profit I do this for the love of coding. I'm a Painter & Decorator/General Builder (Jack of all trades, master of none lol) I code to relax and stress my brain a little, mental gymnastics, keep the old grey matter ticking.
I cant really call anything "official" unless its endorsed and promoted by TGC, again I'd be happy to DLC it and earn a few pound notes but that was never my plan, my intention always has been to make AppGameKit better today than it was yesterday because I want this product to succeed and stay relevant, TGC being a British firm and all that post Brexit stuff (yea, I'm a nationalist, sue me! lol)
As for the render engine it does not matter as this is pure WinAPI, well, 95% I do of course need some of PB's lib functions, Nuklear is fantastic and my plugin is in no way a substitute or replacement its a different beast entirely, IM mode UI's are great but still a learning curve for those used to Retained mode UI's plus a MDI (multi document interface) and MMS (multi monitor support) is impossible with IM mode (I know IMGUI has that docking thing which looks fantastic but Nuklear does not).
I don't ever see TGC adding a native UI solution as its a massive amount of work, Win32 for windows, GTK for Linux and god knows what for MacOS, then Android, IOS, Py, HTML5 .... the best we could ever hope for is a cross platform IM mode that still poses the MDI and MMS issues, maybe a wrap of wxWidgets or QT ... Not sure if that covers all platforms though, so to be honest I give TGC a pass on this one as its a big ask.
As for the plugin itself, I found the issue with closing a parented window I was right it was a flag issue (as most things are in WinAPI) and I am working on expanding the menu functionally to support sub menus, then the toolbar should not take to long its a simple API for that, I looked at ribbons but don't think I will add them as A. I don't like them and B. the API is a complete mess, when I have something I consider to be stable I will post a WIP thread ... its getting close to that target, I'm pulling the public repo for now though as the current code IS unstable.