Challenge is when more aircraft does it simultaniously, declare emergency.
One aircraft declaring emergency is relatively easy to handle, but if several aircraft follow, due to a "he did it, then I can do it"-mindset, it may spark a lot of problems, especially for those who are in the most dire situation, since they may end up behind someone who could have been in holding for an additional 5-10 minutes.
Not saying the mindset is something that is likely to happen, it's may still be a danger.
Like LookingForAJob said.