Wow! Since hackaday published an article about this project ( https://hackaday.com/2019/10/14/repurposing-a-toy-computer-from-the-1990s/ ), messages come pouring in from all over the world! And it fills me with joy, how many people like this project and have even already done amazing research in the same direction.
Worth mentioning is the work done by @Alex Rider about the french "YENO Compusavant". which seems similar to the "Genius Leader 6000 SL". Check out his website for more info: http://alexandre.botzung.fr/
I think I will be setting up a Github repository to merge all findings in an "(Unofficial) V-Tech 8-Bit DevKit".
So: Stay tuned and stay curious!