It's not KYC because they don't require to know you. You're more than welcome to use a VOIP virtual number or pick up a burner. Signal added usernames as well for times when you don't want to give people your number. You're right that currently the only payment method they offer is Google Play but it uses the same zero knowledge proof as their secure donation system so they don't know who you are. But I'm with you on that, its not ideal. What is ideal though is that all of my friends and family can download Signal and message me with my phone number straight away. Again it's about reducing the barrier to entry.
How is Signal a honeypot though!? How do you think Signal might be used against an individual?
