the 4mb bloat has been evaluated.
the main cries over the last few years why anything above 1mb was bad was things like
"not everyone has fast internet"
"chinese firewall"
etc
yet all that has been debunked and tests were done that 8mb is acceptable.. but 4mb was deemed the very safe amount to handle for now as acceptable bloat.
"chinese firewall"
yes thats right. while the west was crying that it cant go above 1mb due to chinese firewall.. the east (inside the firewall) all laughed and said what a stupid doomsday. nothing about the chinese firewall has issues with it and data can be so much more than 4mb
"not everyone has fast internet"
tell that to the millions of people in africa doing skype videocalls. then millions of people uploading to youtube. millions doing livestreaming, whilst online gaming...
so devs now backtracked doomsday and happily said upto 4mb bloat was acceptable.
yet still keeping tx baseblock data at 1mb..
i cant wait until they backtrack the 1mb baseblock dooms day when they finally see its just a orphan risk scenario.. hense the need for super high majority consensus to mitigate orphan risk.
the 'it causes altcoin' doomsday is FUD. because oppositions need EXTRA added code to intentionally IP/USERAGENT BAN connecting to certain nodes.. just like ethereum intentionally split '--oppose-dao-fork'
without adding an intentional ban list of IP/useragents. the connected nodes just have an orphan battle on a single chain, they dont keep 2 chains alive for eternity they orphan the minority
high majority consensus means low risk of orphans. and leaves the minority never syncing.. thus again no second chain. just minority left unsynced
as for the "linear/quadratic" doomsday.
easy.
if sigops is causing issues... limit sigops.
there is no rational reason for one person to need to do 500-20000 sigops. so limit the number of sigops a tx can have.
aswell as ensuring validation times are not used as a DDoS, the extra benefit is we will not see a block with just 1tx sized at 1mb with hefty amount of sigops to churn through..