Mostly just time and testing coverage, and more packages for various things. Maybe another 10,000 man-hours? I don't know the exact numbers.

For context, I've found and/or helped fix bugs around multi-char string split, process termination on windows, and async IO on Windows. All things that forced me to pop the hood on the language, study relevant OS APIs, and generally yak shave, rather than focus on the task at hand. Which has been really edifying, but would have slowed me down if I was writing for a job.

In the process, I've written a few libraries of my own for things like string manipulation, data schemata, rendering html forms/tables based on a schema, and so on.

If you have people that are competent with C, then Janet atop that could work well, but by itself, it's still a long ways from having all of the things one might expect from Python/Ruby, let alone Java or .NET