Having non-destructive editing and all objects are scalable vectors that offer bit depth independence was in TIFFany 3.0 back on NeXTSTEP in 1996. I actually demoed it as an Apple Engineer from NeXT to the Adobe Devs who later incorporated it into Illustrator and Photoshop.
Having the ability to truly work with such functionality would give MyPaint a huge presence in scene development for Games, Motion pictures, etc. You would want a live edit view with minimal post processing and a post process view for final output. Not having the ability to treat all objects as scalable and independent is one of the reason Inkscape was developed. However, they have a lot of limitations in that application. To build upon libraries and cross service functionality between GIMP, Inkscape and MyPaint would be a big selling point for FOSS.
On OS X working in Affinity Designer and Photo, with Pixelmator allows for a great work flow. Vector Brushes in Affinity Designer is something that would make MyPaint an obvious choice to have. The traditional painting of MyPaint is awesome. It just needs that added underlying large functionality to be an indispensable tool in more market segments.
However, I would first coordinate with GNOME/KDE and Linux proper to get a much broader range of Tablet/Pen functionality to not only recognize the USB device, but actually leverage the hardware and use it as designed.
Like Wacom, Huion should be built into GNOME and KDE. As of now, it’s hit n’ miss.
MyPaint needs a proper port to OS X that GIMP already has done. Elle Stone and Partha seem to be the folks to work with to get it done.
Long-term, I would love to see Blender, GIMP, MyPaint and Inkscape as a quartet of tools used along side Adobe’s traditional suite.
Final Cut Pro/Motion/Logic and Adobe Premiere will never lose to any FOSS platform. The previously mentioned quartet has the best shot of garnering major financial backing, while maintaining your core ethos on licensing, if you can collaborate together more completely.