Also, Python would have been better than BASIC as the built-in default language.
If you want Python just use modern laptop, no need to retro anything.
BASIC has command-like statements, no complexity like lambda, classes, modules, etc.
Just not having line numbers cooked in is a total game changer.
And no GOTO.
If they upgraded the C64's BASIC to 7.0, that would already make a lot of things much more accessible.
Yup, even for the old 8-bit computers FORTH would've been a lot more elegant than BASIC. But back in the day BASIC came with highly valued conveniences such as a soft-float implementation that meant support for the "desk calculator" use case was available out of the box, and users could just go on from there.
No idea what this BASIC looks like though; the documentation seems chaotic and hard to access. Just saying that BASIC does not necessarily mean the BASIC that you or I used back in the day. I also agree that you can do a hell of a lot better than Python to introduce programming to kids.
Important thing about BASIC is that each "command" does a rather limited amount of "stuff". In that way it is kinda similar to assembly language.
It encourages the user to learning programming and develop their own apps.
IMHO, humanity is yet to build a better beginner language, at least if you look at the late BASICs such as QuickBASIC.
Besides being integral to the experience / faithful to the prototype C65, it is remarkably reliable storage media that's well-suited for this class of machine, which have very few KBs of RAM.