As far as the tax: personally I'm very in favor of slowing down trading... unfortunately, what's being proposed introduces as much structural game theory as it eliminates. What's the dominant strategy for a trader faced with a rule like "any trades resting for less than 300 micros get taxed"? To be as fast as possible without triggering the tax; staying just above the threshold.
All that economic waste on low-latency tech will just be redirected to low-jitter tech. Those who can reliably land an order within +1 microsecond of the tax line will outperform those who only have an accuracy of +10.
I'd like to see more exchanges experimenting with things like random variance in speed bump size, frequent batch auctions, etc.