So that particular calculation for automatically "adapting" is simply an example of why I am doubtful that automation is the way to go, since basically all it amounts to is carte blanche for all miners who want mining to be limited to a privileged elite can simply spout the biggest blocks permitted, constantly, thus automatically driving up the size permitted, letting them spout out even bigger blocks and so on as fast as possible until the few of them left are able to totally control the whole system in a nice little cartel or oligarchy or plutarchy or kakistrocracy or whatever the term is for such arrangements. (Sounds like an invitation to kakistocracy actually, maybe?)
Basically automatic "adaptation" seems more like automatic aquiescence to whatever the cartel wants, possibly happening along the way to leave them with incentives to maintain appearances of controlling ess of the network than they actually do so that if/when they do achive an actual monopoly it will appear to the public as maybe pretty much any number of "actors" the monopoly chooses to represent itself as for public relations purposes. (To prevent panics caused by fears that someone controls 51%, for example.)
-MarkM-
If they manage to do that in such a way that keeps
global orphan rates down and the difficulty at least stable (so this would have to be done slowly) all while losing boatloads of money by essentially requiring no transaction fee ever, good for them. Other 51% attacks would be more economical, especially since this attack would be trivial to detect in the non-global-state side of things. For example, people would notice a large amount of previously-unheard transactions in these blocks, or extremely spammy transactions. Worst-case, they could get away with including all legitimate transactions and a small amount of their own and not be detected, raising the limit to have a block be able to contain just above the amount of typical transactions made per block period.
However, other considerations can be added. That suggestion is by no means final. Some extreme ideas (not outside the box, I know, but just to prove that this attack can be prevented with more constraints):
*To increase max block size, global orphan rate must be below 1%.
*To increase max block size, 95% of the blocks in the last difficulty period must be at/very near the current max size.
*Max block size can only increase by a factor of 2 over four years.
For more ideas, think about the process of raising the block size limit in manual terms. What would/should we consider before manually raising the block size limit? Let's see if we can codify that...