I've had trying Bolt out on my very long Trello backlog for nearly 6 months; have been looking for a CMS that's not WordPress and yet able to handle custom post types well. Bolt does have a bit of a learning curve due to the sheer genericness and flexibility built in, but it looks promising.
I don't think it is quite a replacement for WordPress though. Plugin ecosystem aside, and it really is amazing what you can arm-twist WordPress into doing, the 'ethos' of Bolt is a little different, as seen in this discussion on Github Issues. Most obviously, it may or may not be a good thing that most of the config is done in YAML: I like the idea, having built a mini web service tester once that takes a huge JSON file as input, but it's not quite as friendly to non-technical people who're not used to being very exact with whitespace, and also doesn't expose all the options to you. Sublime Text has a similar issue with its JSON configuration, but at least it has the '- Default' version of the JSON config easily available for you to load, compare and search through.
As mentioned on the Github issue, there's also nothing similar to the 'widget' configuration available in WordPress now. You can still make it happen, just that you don't have nice ajaxy forms that do it for you. Instead, you have to know HTML and the Bolt contenttypes/records engine. That's a tradeoff based on the target audience.
WordPress has a distinctly different audience group compared to Bolt, and everyone is better off as long as they understand that.