alt Hacker News...I'm pretty sure the same would be true in any modern version of NeXTStep had it survived as its own 'brand' (apart from slightly different requirements caused by the hardware the OS needs to run on of course - e.g. running on a handful different Apple devices versus having to work on 'everything').
Darwin ditched the old driver stack for IOKit because they thought it was icky to have ObjC in the kernel. That's pretty much entirely up to leadership changes, not technical reasons.