I think there will be multiple tools for Next available, some leaning more toward windows, some more toward being portable... (I personally have only linux machines at home, so my preference is obvious)... and I don't think there will be single "go to" package suited for everyone, as people prefer different tools and UI. I can sense a good-will underlying your comment, and logic, but that alone is not enough to make such tooling available.
Then again *"The average Windows user won't install Linux just for Next development."* - why not? It's few more click and it's free. I'm certainly not going to install windows, as that's not free and requires license and source code is not [easily] available. But setting up virtual machine with linux is like one evening job, if you didn't do it before (or 2-3h including customization and setup, if you know what you are doing, bare install is like 10-30min). Then again most of the "linux" tools are often written in portable way, often having windows binaries directly provided by author, or you can compile them yourself. I mean, as a windows user you will have probably much higher chance to run all of the tools, including linux ones (contrary to linux users). You are just missing modern OS goodies.
Also you are not dealing with "average users" as users, but SW developers. The core team will surely want to cater for newcomers and give them some reasonable kick-off on the machine itself, including Next BASIC and manual, but that's long way from "commercial development" and it will still take huge effort on their side to deliver even that startup pack (especially in similar quality like the machine case
While seasoned Spectrum developers are not truly depending on any external tools, they were writing games back in times, when many of them wrote at least one own assembler in their life, not only not afraid to create their own tools, but often stubbornly preferring it precisely that way, writing everything own and from scratch.
Considering what tools are currently already available (z88dk, pasmoNext, CSpect, snasm, Boriel IDE, ...), I think one who is determined to actually create something on Next can and will find a way. If none of those tools fit your needs perfectly, and you would rather wait until such perfect one emerges, I'm afraid that may be also lack of the required determination level. Because developing for Next will have quite some learning curve. The ZX machines are quite easy to learn basics (I would say even considerably easier than modern educational platforms), but difficult to master (and I don't think any tool alone will ever close that gap completely, surely good tools will help, but there's lot more to it).
I would recommend to try Next BASIC first to do some introductory tinkering, and not to worry about compilers for the moment. It may give you better idea for later, what precisely you need, and explore further tools later.