1.) Wazapp nightly build 35 is working just fine for me. Use the registrarion link found on the Wazapp thread to register.

2.) The future for the N9 has been bleak since before its release. API's will change eventually, things won't be compatible and things will cease to "work." It's up to individuals to make the necessary fixes and updates when that does happen. I can't say for certain who would, can you?

Nexus 5 will definitely be more "futureproof" than the N9. Which one should you get? That's up to you.