A taxation will accomplish next to nothing except to hurt newer players even further. Using myself as an example. I have over 300M. What system could you implement that would remotely phase me without seriously impacting the enjoyment of players with nowhere near my gil count? 1M gil per month wouldn't even dent my total. I made that back selling the Troll mount from Unreal farming. If you push that number higher, it'll make housing near impossible for most players to maintain - especially nowadays when crafting is near worthless in terms of profitability.

All this does is punish players who don't have loads of gil saved up and encourages RMT. I can guarantee you people will pay real money just to offset the rent fee.