I see this milestone on Github that is fast approaching: https://github.com/gohugoio/hugo/milestone/88
Hugo is already very feature rich and 1.0 is more of a psychological milestone rather than a technical one. There is no limit to features that can be added and Hugo is very stable.
In case the Hugo team is planning to do a 1.0, I would request them to take a look at the API and figure out what needs to be deprecated from the longer term maintenance perspective so that we can have breakage sooner rather than later.