I will be coming from an HTC One that I have RUU flashed to be a Google Play Edition. I'm enjoying stock Android, even though I do really like Sense 5. I think stock Android will be even better on a device that was built for it from the beginning.
Enjoy your Moto X. I hear it is a great phone. I'd like to get one but they want too much off contract compared to what the N5 will likely cost if it follows the N4 model.
You could always RUU flash to GPE software to get you by till then.
The Nexus 5 will not have an SD card slot. I'll eat this post if it does. Also, while certainly possible, I'm extremely skeptical of those saying the 32GB version will have a larger battery than the 16 GB. I'd love it to be true cause I'll be getting the 32 either way, but I seriously doubt it.