i reviewed all 3 links you referenced but none of them had a big warning that someone could hog up an entire 4MB block with a single transaction or that people could use the witness field to store pictures and audio and video clips. was that supposed to just be understood and assumed that everyone knew those things could happen and was ok with it without even mentioning it at all? i don't think people are that smart, in general. but the developers should be. no question about that...
Including single TX (excluding coinbase TX) always has been possible if miner/pool wish do that. But i guess even developer don't expect witness data would be used to store arbitrary data. Although this link mention 4MB block is possible if it's mostly contain witness data.
Is the segregated witness soft fork equivalent to a 4MB block size increase, a 2MB increase, a 1.75MB increase, or what? I keep hearing different numbers.
The current proposal for soft fork segregated witness (segwit) counts each byte in a witness as 0.25 bytes towards the maximum block size limit, meaning the maximum size of a block is just under 4MB.
However, blocks are not expected to consist entirely of witness data and each non-witness byte is counted as 1.00 bytes towards the maximum block size limit, so blocks near 4MB in size would be unlikely.
According to some calculations performed by Anthony Towns, a block filled with standard single-signature P2PKH transactions would be about 1.6MB and a block filled with 2-of-2 multisignature transactions would be about 2.0MB.