If this gets implemented, in the current form, people will start moving 10btc to addresses so that they can sign them for different users, for a fee. It'll be something like the current situation of account selling, it's not prohibited because it can't be controlled.
That's not necessarily a problem - the point of this subboard/new forum is to only those actually IN bitcoin, aka those that understand how it works, and have actually put $X amount of fiat into it.
But yet, it
may be is a problem, as this can be a method for people to get in that forum/subforum, without actually having 10 BTC, but rather paying a fee(say 0.01 btc) to someone who will sign a transaction with an address that has 10BTC on it.
Example:
1. Alice has 10BTC and sells signs messages for users to get into the 'Elite forum'.
2. Bob wants one, pays for it and gets access to the forum.
3.
4. Profit.
Conclussion:
Bob gets access to the so called 'Elite forum' without actually owning 10BTC.
Alice gets some 'passive income' from owning 10BTC.