I think it depends on the adoption of Linux on the desktop. When more people get a taste of what freedom of software brings, they are going to want that for their phones as well.
That or we might just be years away from the next big thing where everyone walks around with AR glasses and the cycle starts all over again with companies competing for a duopoly, and we’re just fucked.
I hate the fact that none of the big names support CalDAV natively. DAVx5 is cool and all, but app developers really need to step up their shit and support CalDAV already. Not just Microsoft Exchange and Google Calendar but CalDAV as well. It’s not like they need to rebuild their apps from scratch.
At this point you might just be better served using a web app instead of a native mobile app. Maybe K-9 Mail transformation into Thunderbird Mobile might bring some good news, but I’m not holding high hopes.
Maybe we should, under the EU’s DMA, force anyone that bundles a calendar/note app with their phone OS to support CalDAV as well as any proprietary protocol of their choice.