Deterministic Tie Breaker. My understanding is that whenever honest miners see two competing chains on the same height, they will deterministically select one of the chains as preferred chain. This is in contrast to the current solution where miners prefer the chain first received. This change ensures that all honest miners agree on the tip of the chain, in cases where it is ambiguous.
In a benign network, where everybody acts honestly, this would reduce unfairness. But as a pool operator I would certainly modify the software to prefer my own block instead of discarding it. If all pool operators think like me, we’re back at square one regarding fairness.
Regarding selfish mining: I assume you’re familiar with the attack models of Sapirshtein/Sompolinsky/Zohar or Bar-Zur/Eyal/Tamar. They give the attacker some means to reorder messages: if one block of height n shows up, they can send their own block of height n (if they have any) with the MATCH action. Fraction \gamma of the defenders will continue mining on the attackers block. If you now add your hash-based tie breaker, this reordering will work in 50% of the cases and should be at least as bad as assuming \gamma = 0.5 in the other model. I say at least as bad because the attacker knows in advance whether the MATCH will work and probably can adjust his strategy based on that.
Uncle+Orphan rate. I’m not sure what you mean with uncles, as Tailstorm does not have any. It has trees of k subblocks between each pair of summary blocks. It discounts rewards based on the height of this tree. Probably you mean, if the subblock tree has height k - i, there are i uncles on this tree? Then the uncle+orphan rate in tailstorm with subblock interval n seconds should be about the same as the orphan rate in BCH with n seconds block interval. Assuming propagation times of Tailstorm subblocks and BCH blocks are the same.
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