On Aug 7, 2015 11:19 PM, "Sergio Demian Lerner via bitcoin-dev" <bitcoin-dev@lists.linuxfoundation.org> wrote:
> b. Reduce the block rate to a half (average 5 minute blocks)
>
> Suppose this is a one time hard fork. There no drastic technical problems with any of them: "SPV" mining and the relay network has shown that block propagation is not an issue for such as small change. Mining centralization won't radically change for a 2x adjustment. 

I don't understand this. All problems that result from propagation delay are literally doubled by doing so. Centralization pressure results from the ratio between propagation time and interblock time. Efficient propagation algorithms like the relay network make this presumably grow sublinear with larger blocks, but changing the interblock time affects it exactly proportionally.

All problems that result from propagation delay are literally doubled by doing this. Doubling the block size has a smaller effect. You may argue that these centralization effects are small, but reducing the interblock time has a stronger effect on them than the block size.

Also, you seem to consider SPV mining a good thing? It requires trust between miners that know eachother, and fundamentally breaks the security assumption of SPV clients... and if the propagation/interblock ratio was lower, SPV mining would have less effect. I'd say it is exactly a result of the centralization pressure we're trying to avoid.

--
Pieter