It seems to me that this is an industry saying what it wants without thinking about what the people want.
Why would members of panels want to agree to be on a central register (and I suspect that European law would require their permission)?
The cheats don't want to be caught.
Honest people might not want to be on a central database. If I sign up to panel company X, in the UK, because I like them, do I want to be on some central list, possibly stored outside the UK? Would I believe the people who might run it when they say my information would be safe with them. In the UK we know our information is not even safe with the Government (they lose CDs storing the data), and companies like Microsoft, AOL, and Google have all had embarassing loses of data security.
We might like a central list to flag up cheats, but would we be able to maintain the legal level of proof to say somebody is a cheat, or perhaps that they do not pay enough attention when they do surveys.
If we find they are on 20 panels, do we reduce the number of surveys they are offered, and if we do might we run the risk of court cases alleging loss of income due to anti-competitive activities.
I think we should start by realising we are not hold the Aces, we need to persuade people to co-operate with us, and we can't regulate our competitors.