This, one of the key perks of Sandstorm.io is that you can use apps written in any language that runs on Linux pretty much.

Cloudron.io is fairly similar, though makes some different design choices.

I definitely like sandstorm approach over nextcloud plugin model that tries to make nextcloud do everything. It's a security nightmare

I do too, and I feel Sandstorm has the superior security model of most of these platforms. But a key perk of Nextcloud is that it can be installed on cheap shared hosting which doesn't grant the customer root access.

Sure.

Still, NextCloud provides the most popular cloud stuff for non-techies: Storage like Dropbox and adressbook like Google/Apple.

Do you know how well NextCloud works in a home environment? Is it really easy to automate the punching of a hole in the home firewall to allow access from anywhere? If you know of a project that automates this punching, it's a great combo to nextcloud.

I punched the hole manually. Unfortunately, even this is not enough. The tricky part is to have the same hostname inside and outside of your NAT.