That's fine-- I totally understand. It's not built for everyone. Cloud Sync is needed for features like Snoozing and Send Later. (And more things upcoming...)
Have you guys thought about maybe bundling a local sync engine with the electron app or streamlining the setup and integration process for a local sync engine some other way (a pull-able Docker container comes to mind)? That would definitely make Nylas a lot more attractive for privacy conscious users like myself.
What specifically have you had issues with? We haven't seen great proven cross-platform support for docker images, which is why we're still using Vagrant+Virtualbox. From the folks we've talked with, it seems to be a pretty painless process. (We do this for development all the time.)
Obviously features like Snooze and Send Later won't work, but the idea here is you can build the entire stack or deploy it to your own VPS at any time.