The problem with the flat fee becomes apparent when you look at a wealth distribution graph

I doubt the top % will get involved in mining. They will use the network the 90% works to keep alive, to make billion $ worth of transactions for 0.001 BTC each, while most people transact in 100-1000's, and pay 0.001 BTC each.
A % fee makes sense from so many points of view in the long run, and by this I mean really long run, several generations maybe.
Anyway, since the coins is born as a token and because I really like waves so far, transactions for a nominal 0.001 WAV will always be possible. It's only a small step in the right direction.