Pushbullet already pushes out (no pun intended) features at an alarming pace, but if you need to be at the very edge of development you can now participate in their beta program via Google Play. It’s as easy as joining a beta program has ever been — join the community here, then opt into the beta here. Simple, no?
From there you’ll be delivered updates of all the latest features before they’re ready for gen-pop. They also announced an update to their Windows app that adds support for notification mirroring so be sure to check that out if you’re into that sort of thing.