The chosen curve was mainly selected because it has weaker security, and since we were aware that similar curves exist, this one had better support for the proof of concept implementation.
The idea of having multiple canary addresses is a good one and was never discarded. However, there is also the issue of how much the reward would be split. If the idea does not gain enough traction, the canary bounty being split among multiple addresses might not be sufficient to trigger a CRQC.