"the formation of the Julia Computing group has made Julia's development a bit of a walled garden".

I'm not sure what you mean. As far as I can see, Julia Computing is not rich enough to take over development of the language, even if that is what they wanted to do. It's just a way for those guys to get paid for their full-time commitment to Julia, and a fairly standard one, as far as I can see. Language developers that aren't funded by a large existing company tend to do consultancy to pay the bills.