Email that is reliant on the cloud is dumb.
A raspberry pi has more processing power than's needed to search and store email. ... etc etc
This trope is absolute bullshit. What people want is for stuff to work and, if stuff doesn't work, for it to be someone else's fault and/or be easy to fix.
Self-hosting fails massively at the second criterion there. Right now, if a cellphone breaks, you can just get a new one and your contacts, messages, apps, etc all sync back to it. Done, you're back on your feet.
If you have self-hosted email or smart-home-stuff, the failure modes are much worse, and you're far less likely to have someone else to blame.
Also, a raspberry pi does not have enough power to do good voice recognition, not to the level of siri/alexa/google.
It also doesn't have enough storage to cache all your music, videos you may wish to play on the TV, etc, so some external cloud integration will be needed regardless.
Self hosting has failed. People use gmail, not postfix. People use spotify, not cds or local mp3 players. People use netflix, not blurays. People use google search to find previously seen info, not a locally saved and curated archive of websites or a home-grown card catalog system. People use facebook to communicate, not diaspora.
> it is trivial to create a more user friendly device
This is obviously false or else devices like this would have been trivial to make and seen some success... but things like sandstorm.io, yunohost, and others have been incredibly complex projects and have not really succeeded. It's clearly not trivial since those people have collectively thrown millions of dollars and dozens of man-years at the problem with no glimmer of hope.
The closest we have to success in this space, I'd say, is NASs which ship owncloud... and those have not caught in for the average household at all.