You get almost all of that with the more common language options too (MicroPython, NodeMCU/Lua, Espruino/JS). What makes this custom language better?
If you have a bigger machine you can optimize some of this (V8), but these optimizations typically need memory and/or a JIT. (And Python struggles to optimize even on stronger machines).
By starting from scratch (with what we learned from V8 and Dart) you can design something that feels similar but is much cleaner and faster to run.
Besides that, there are other languages that have similar characteristics. Wren (https://wren.io/) is pretty nice but doesn't have type annotations or explicitly target embedded.