If segwit activated and spammers still able to spam with old keys then every one should switch to segwit and then everyone could ban/ignore those spams
getting everyone 46million output to move to segwit keys. would in itself cause a mass 'spam event'....think about it.
secondly then rejecting old transactions is just killing off the hoarders that are not actively spending.
thats like nuking someones old safety deposit box purely in the hopes it will reduce the queue at the banks cashier desk because savers who hardly ever/ dont move funds are then lost.
wake up
far far far easier to not give spammers too many opportunities.. rather than open new attack vectors and then build walls affecting innocent people.
EG
core v0.12
a spammer could fill a block with just 5 bloated tx's of 4000tx sigops. (20k block sigops)
core v0.14
a spammer could fill a block with just 5 bloated tx's of 16000tx sigops.(80k block sigops) meaning...
..yep core 0.14 makes a block have alot longer native quadratic validation time attack.
however. instead of locking out old UTXO's completely as a fix ImHash said..
keep the 4000tx sigops but grow the (80k block sigops) meaning now requires 20 bloated tx's to fill a block instead of 5 and the time is better and manageable,
yep
20 x 4000=80000 is better by many factors of multiplication, rather than
5 x 16000=80000