The title says it all, the way I understand it is that SegWit2X is SegWit then the block increase comes after a few months, 2mb blocks instead of 1mb. In the other hands, isn't SegWit alone supposed to make the block like 2.3mb technically? I saw some people saying that Luke Dashjr call it 8mb as well (and not sure why) so I'm a little bit lost.
segwit activation alone means base block is 1mb... and while the segwit keypairs remain UNAVAILABLE(yep wont be available untill well after activation) the witness are remains unused.. so total serialised weight is 1mb max
later segwit keypairs gets released and a onslaught of people moving funds to segwit keypairs (addresses beginning bc1) which starts using a bit of the witness area, meaning
if 10% of the base block is segwit (bc1 addresses) then witness area becomes ~0.1mb making total serialised weight is ~1.1mb
if 100% of the base block is segwit (bc1 addresses) then witness area becomes ~1.1mb making total serialised weight is ~2.1mb
if segwit2x (the 2x part(2mb base)) activates 3 months later meaning the base block moves to be able to be 2mb max
then depending on how many transactions in the base block are bc1 based(segwit keypairs) then decides how much of the witness area is used. which then determines how much full serialised data it really consumes
the reason for the '4mb' weight (pre2x(2mb base)) and '8mb' weight (post 2x(2mb base)) is that thise 4/8 numbers are mainly 'buffer' space like having a 1tb hard drive but only ever using 500gb
the stats of average real transaction utility during the pre2x period, and IF 100% of base block transactions are segwit.. is 2.1mb serialised data, the spare 1.9mb will probably be used for crap like gmaxwells CT pederson commitments (confidential transaction bloat)
the stats of average real transaction utility during the post2x period and IF 100% of base block transactions are segwit.. is 4.2mb serialised data, the spare 3.8mb will probably be used for crap like gmaxwells CT pederson commitments (confidential transaction bloat)
