- Have devastating effects on the fee market
Since there's more space in each block, this space is now less valuable, fees might not be zero, but they'll be lead down to the minimum and competitiveness for fast transactions will be dead.
I don't know how it would change the fee market.. There hasn't been any scarcity in blocks before so fees would probably stay quite similar to what they are today. If adoption continues to increase, the total of collected fees will be higher as there would be more transactions per block.
Wrong. Some scarcity in blocks, and some disparity in the fees paid is essential to maintain a healthy economic relationship between the miners and the users. More tx volume just recreates today's dynamics on a larger scale. As the block reward subsidy diminishes, the extent to which that subsidy was distorting the fee market will become increasingly more apparent. When the block reward approaches zero, having a functional fee market in place is the only way of incentivising miners to mine at all.
Treating fees as "one-fee-fits-all" doesn't take account of the economic reality. Some transactions must confirm ASAP, for a wide variety of reasons. Others can be afforded hours, days or perhaps even longer than that.
Funnily enough, that's why no one is saying let's get rid of the cap entirely. No one's saying let's have 10GB blocks tomorrow. Everyone who isn't a perma-1MBer knows that the limit needs to be raised, but everyone seems to have a different idea on how much of an increase is safe. I honestly don't see 8MB as a threat to decentralisation. I don't see how anyone could. I'm not entirely convinced about the doubling part being needed yet, but we don't necessarily have to allow the doubling to happen. It can be prevented with a soft fork if it isn't needed. All things considered, BIP101 isn't the catastrophe some make it out to be. It certainly doesn't guarantee a future of 8GB blocks and half a dozen nodes running the whole network, no one in their right mind would allow it to come to that.
Some do advocate for an infinite limit, but they're in the same category as the 1MB'ers IMO (i.e. not credible insignificant minority). 8MB/BIP101 won't cause heinous problems tomorrow, but it's the progression of that schedule that will really cause issues (as you concede).
Looking in the Bitcoin github, there's an effort under way to develop a specific test harness for the testnet network, in order to simulate these various schemes and schedules on an actual network. It will be interesting to see the results once that effort is ready to conduct the tests.
But if the miners aren't showing much support for BIP101, I'll go along with that. Their preference seems to be BIP100 at the moment, but there are justified concerns that they could choose to enforce a 1MB limit forever if that's what they deemed most profitable for them. What would be beneficial to the network as a whole isn't taken into consideration at all and it involves placing trust in an entity to set a variable which dictates how the network is run. I would feel much more comfortable if this was done algorithmically, like just about everything else in Bitcoin.
That's similar to my position also. I support an algorithmically determined blocksize limit, but sadly we don't have any complete proposals yet. Greg Maxwell and Mark Friedenbach have their FlexCap scheme floated, upal's Dynamic Resizing concept is out there, and I think Meni Rosenfelds's idea has been a little neglected (he tabled it early on in the debate, so it's understandable).
The problem is that the code for these proposals doesn't exist yet. But it will emerge, the FlexCap idea will almost certainly receive a coded implementation.
More than ever, I'm convinced that the answer lies somewhere between BIP100 and upal's BIP1xx. A balance between the two is absolutely 100% reasonable and the only people who would still take issue with it would be the ones who think Bitcoin's sole purpose is to benefit a small minority of ultralibertarian crackpots.
That sounds like a sensible position (although I don't understand the political allusion, libertarianism doesn't contain any economic or computer science theory, those being the disciplines that pertian to the blocksize debate).