As many of you know, Bitcoin Unlimited is gaining momentum with miners, roughly has 30% of the hash power presently (based on last 1000 blocks, slightly more if you only go back 144 blocks). Additionally, 8 MB block miners have a small but not negligible percentage of the hash power.
There seems to be some confusion about how the fork would take place. It actually is fairly well thought out:
https://medium.com/@ViaBTC/miner-guide-how-to-safely-hard-fork-to-bitcoin-unlimited-8ac1570dc1a8#.t7nul1uz0There are three steps the fork.
In the first step, miners willing to mine BU blocks simply indicate their willingness to do so. Many of them that are indicating a willingness to do so are probably actually running core, they do not need to upgrade in order to send the flag and it would be expensive to update to BU only to have to revert back to core if BU fork does not happen.
It is not possible to accidentally indicate support for BU, so any miners sending the BU flag are doing so intentionally and thus indicating intent to mine bigger blocks, and that is enough right now.
If 75% of the hash power indicates support for BU consistently for an entire difficulty period (2016 blocks - typically about two weeks) then they enter step two.
For step two, users are prepared for the fork. This will take two difficulty periods (four weeks) giving ample time to get the word out letting users know they will need to run a client that accepts larger blocks. During this four week process, they must maintain 75% of the hash power or the fork does not happen.
So, from the time that 75% of the hash power indicates intent for BU to the time it actually happens is a minimum of three difficulty period, a minimum of six weeks. During that 6 week period, miners that indicate they are with the BU camp will still orphan any blocks that are larger than 1 MB unless it is part of a longer fork with 6 confirmations, and that will only happen if 51% of the total hashing power activate early, not likely to happen.
Once that phase two has passed, then miners will optionally indicate that they are willing to accept blocks larger than 1 MB and build upon them. However the actual fork will not happen until 51% of the total mining power has indicated they accept blocks larger than 1 MB.
It is possible for that to never happen. One malicious scenario is 25%+ of the current mining power indicates they are with BU but is lying. That could prevent the needed 51% of all hashing power needed for a fork to become the longest chain. I doubt that will take place, that would be a conspiracy on par with censorship of users voicing their opinions on Bitcoin related forums. Oh, wait... that's even happened to me. Well anyway I still doubt that will happen.
Once a chain with six blocks built upon a block > 1 MB exists and is the longest chain, then even BU miners who have not changed their configuration will accept it as the valid chain and the fork has taken place.
That is how it will happen. Agree with it or not, it is very well thought out and avoids activation unless there truly is miner consensus on the BU fork.
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What does that mean for you, the end user? (and me)?
Run a BU client and whether or not it happens, we are fine. It takes 95% of miner consensus for SegWit to activate, and that clearly is incredibly unlikely to happen. Even if it does happen, we can still use Bitcoin with a BU client - just keep using traditional addresses and you don't need a SegWit capable client, but since miners getting anywhere close to 95% support of SegWit is much farther off than miners sustaining 75% support of BU - there is absolutely no benefit to running a SegWit capable client now unless you are a developer using the test network.
