When it comes to having a quality laptop and OS to get work done, I would at least be happy with stagnation if the stagnation point occurred around the era of the best MBPs -- late model MBPr 15s, ~2012 to 2015-2016. I'm typing this one one right now. It's a little long in the tooth, but I'm horrified to update to a newer one and have to get the whole bottom panel replaced, yet again.
I'm hoping to defer this decision by a year or two, but I'm sure I'll have to bite the bullet eventually, and every year, I hope that it's not going to be worse, so that it'll at least be good enough. Sadly, it looks like that hope may yet be naive.