Kindles were the only devices that had a fully locked on ecosystem, yet no device lockin on the parent side (no need to keep an up to date iPhone just for the parental controls for instance)

Nowadays I think I wouldn't mind audio and video, especially audiobooks and channels like those on Nebula. YouTube is a cesspool while also hosting the most interesting content, running something like Newpipe on a kid's tablet with specific channels locked on would also interesting IMHO.

> addictive games

The main issue for me is the lack of management options. ScreenTime is half-assed, what we have on Nintendo's Switch is a bit better, I'd actually spend time to deal with all the settings and rule system if it was available in a very granular way. We're already spending the same amount looking after other stuff.