In your system (op), I don't see why anybody would want a life time membership. I think, it was making sense for traders to buy one but if you lower so much the fees, there is no inventive anymore.
Why no just lower the "cancel order fee" at the minimum, just to remove all the critics about it and let the rest of the fee structure as it is. At the end of the day, it's very cheap compared to 0.1-0.2% of your filled order if you trade more than 1 btc / trade.