How about only seriously consider appeal if :
1. The member have good reputation or known to help others
2. They have high rank or/and received lots of merit (earned in correct way)
3. Many members agree to unban. This is should be easy and good way since so far i only see 2 banned member got support from other member to be un-banned

Additionally, escrow some Bitcoin is unnecessary and limit to those who have lots of Bitcoin. Simply remove signature space 1 year - forever is easier solution. If the user only care about earn money, he will leave while actual member will stay and continue being helpful.