Here are my unordered thoughts.
So it seems a lot like an improved colab with a deployment stage. Which sounds good to me, it will be much more expensive than colab though.
I like the pitch of SWEs doing ML instead of pitching towards Data Scientists. As Data Scientist turned SWE I still miss the Jupyter like cell based execution. (you said it exists but I couldn't find it.)
In general I'm quite sceptical when it comes to online IDEs. However, for Text and Image based models it might be enough (since you don't need tooo much code).
There might be a valid niche between colab on the one side and building it yourself with AWS cli on the other.
I wonder though, in your target market it really isn't such a big deal to spin up a rest api, there are no lambdas with GPU though (but this should be a matter of time). Or use something like AWS batch for remote training. It will come down to: Is it more convenient to code in your IDE and you handle Lambda, Batch Docker and CD. Or do you code in your own IDE and you have to handle this stuff yourself.
Wish you all the best!