I think Rick Mercer was behind that. That is an example of something that would obviously be frivolous.
One of your safeguards is that by the time it gets to 100,000 signatures, 10 MPs must have decided to endorse it, in the sense of endorse the fact that there should be debate. I assume they don't necessarily have to say that they agree with the content; it's the debate.
I don't see any requirement for this to be cross-party or at least from two parties or at least from one party and have one independent. At the moment you're happy with the idea of 10 MPs, and it doesn't matter if they are all from one party.