Shifter and HardyPress already do so. That gets you all the advantages of static sites, combined with all the advantages of WordPress(ecosystem, tools, affordable labor, easy to use by clients).
Their only major limitation is that they generate/"compile" the whole site, and this takes time.
But that seems solvable by caching(in most cases) and by scaling(which may be easy with serverless). I think it's just a matter of time.
I argue maintainability is the main reason for me to choose Gatsby over WP for projects where the choice makes sense.
You just need to select your plugins from a smaller set, and use external services like disqus for database based service.
And i think with time that thinking could lead to a set of plugins with good security through isolation.
As for hosting complexity - for many sites, this could be hidden from the developer and the client.
And regarding code complexity - how often are custom wordpress plugins or themes(without a site builder) required ? and how much developer time does it take ?