Great talks recently about the best way to set up Grin’s PoW to minimize the disadvantage of smaller players and avoid walking into a 51% attack during year 0.
I haven’t seen any discussion of merge-mining to improve security/distribution. Namecoin did this (with SHA256/Bitcoin) as did Dogecoin (some time after its launch, with Scrypt/Litecoin).
Has this idea been discussed and discarded already, or is it something to consider?
It has not been seriously considered. Grin is expected to be the biggest Cuckoo Cycle coin and to have ASICs for that, so merge mining is something that other coins adopting Cuckoo Cycle should consider. In which case they’d need to be able to link from a grin block to theirs. Right now there appears to be no place in a grin block to inject such arbitrary information, but if demand for that feature becomes strong enough, it will be considered, perhaps in one of the planned hardforks.
Let’s first wait to see how popular Cuckoo Cycle will be among other coins…