It is pretty much the same as 20 years ago. That is, good enough for basic use cases but nowhere near as complete as MS Office. It isn't a serious program for professional use.
It's crazy this hasn't happened yet. Kart racers are conceptually very simple games and are all very similar. CTGP kinda does this but is limited by Mario Kart's engine.
Nextcloud's biggest issue is performance, and PHP, while not a problem per se, doesn't help. PHP is not designed for huge applications that need to have processes running in the background; it only runs when a request is made then stops the process, therefore it needs to load itself from scratch on every single page load.
This is because PHP uses something called CGI; the webserver (usually nginx or Apache) calls an external PHP binary to generate a page. With Go (or pretty much any other language), the app is its own server and can keep data in memory and do stuff even when no request is coming.
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