According to melonDS 0.8ís release thread, this update is a somewhat experimental since further testing is needed to make sure that it works on all setups and OpenGL drivers. Furthermore, some features of the DSí GPU arenít implemented as of right now so some games might have some odd graphical issues but one can always use the software renderer for that.
That being said, Mario Kart DS seems to be running pretty well as per a video attached in the release thread which means that the OpenGL renderer and upscaling are working pretty well provided your PC is powerful enough.

However, there are no public builds of melonDS 0.8 for any of these consoles right now and it must be noted that the PSVita might still not be powerful enough to run most Nintendo DS games so donít hold your breath on that front although the Switch will most likely fare much better.
To grab melonDS 0.8 for Windows or Linux, check out this link. Issues should be reported to its GitHub repository as usual.