Huh? How exactly are they stopping you from sending an encrypted message?

There's no mechanism to decrypt the result before display. So enjoy decrypting AES in your head!

If you're worried about encryption, though, you wouldn't be using their app to display the pushed messages, you'd be using something you control; you only use their push infrastructure as infrastructure.

or just open source

There is still no "compile code, install app, and throw this process on a VPS" solution for pushes, from what I recall

Think of it like email: Email is not inherently secure, but there is nothing to stop you sending an encrypted message via email.

So in this case you would push an encrypted message, and your app would decrypt the message before displaying its contents.

Pushover uses SSL, and then hands off to GCM for notifications. Yes, it's not end to end and you don't control the keys, but it seems to be the best current option and is MILES better than Pushbullet, who have yet to come up with a way to monetize.

https://pushover.net/faq#security

They also have a warrant canary for what it's worth ttps://pushover.net/canary.asc

God forbid anyone know that your battery is low.