I'd take it even further. run a random allocated match no more often than each second. No retail or non-HFT institutional investor would notice the difference

I'd take it even further. run a random allocated match no more often than each second. No retail or non-HFT institutional investor would notice the difference in execution time. Of course, if you do that retail investors would no longer have access to $5 stock trades and actually have to pay for the "fair" services they are receiving. Probably some other cost as well to be absorbed under this model.