If there's anything that'll kill AR before it's really had a chance it's a million different APIs that aren't compatible with each other, leading to developers choosing to support different platforms and users not knowing which one is actually suitable for them.
As for what could kill AR "before its had its chance" (AR has actually been around for a long, long time) - lack of wearable hardware. AR apps on phones/ipads/handheld devices are nice, and getting better all the time, but generally don't have the potential to increase productivity to the extent that hands free glasses/headset can. Wearable hardware needs to get more powerful, less intrusive, and have better/ubiquitous connection (more bandwidth than current cellular, potentially 5G could solve this issue).