Some feedback after playing with it for a little bit with my eight-year-old:
1. The chat interface is a great way to make the old-school console programs more contemporary, while keeping the ease of programming that interactive model. Though my daughter's first thought was to make a friendly bot, which is a bit beyond what she's ready for. The interactive games like Blackjack offer a much more well-defined goal.
2. On our first attempt to extend Basic Chat, we created something like `call chat.say("what is your favorite color?")`... of course we wanted to change it to ask and store it in a variable, but there didn't seem to be any way to edit it to achieve that.
3. Variables confused us for a while. There's no tooltips on the insert panel itself (only in the thing in the lower-left). The cursor didn't make sense as a variable. And then it inserts ??? and prompts for the next symbol, instead of asking us immediately what variable we want to insert. So... maybe prompting for the variable immediately, and perhaps a better button symbol would help there.
4. A "full screen" player would be good, my daughter wanted to surprise me with the chatbot she wrote herself but couldn't without putting her hands over the screen.
5. Getting ideas for what to make is really important. The scope of all possible programs is too much for a kid to figure out. And if they do they'll probably decide on something infeasible. While learning to come up with tractable problems is an important part of learning to program... well, kids need some scaffolding. Scratch kind of does this with the gallery, though as people have become more proficient at Scratch the games became too good. A smaller well-curated list is helpful. You have some, which is a good start. But like Tree Painting feels like a clever but inaccessible example. I'd bias towards simple, somewhat enjoyable projects that are just begging to be improved. The kid should see it and think "I can do better than that!"
6. Coming from Scratch kids are going to be thinking about Sprites. I don't think there's anything like a Sprite or an easy way to create such a thing.
7. I really like the idea of microworlds: coding playgrounds that explore a particular concept. You have drawing and the chatbot here, and I'd love to see more. Like one to do probabilities: it could make it easy to show bar graphs of the results, but otherwise it would mostly be traditional programming. You could do that now with drawing, but the drawing becomes a distraction.
8. It would be nice if you could put pictures in the chat (as output, not letting the user upload an image). Just to open up some other storytelling. This would also require an image editor. Though Google Slides has an easy way to insert images from a Google Image search and the kids make a lot of use of that, something like that could make it easy to add visuals. Or just a bunch of preloaded iconography.
Anyway, a few thoughts, good luck on the project!