I think Hourglass has the highest chances to be activated. Related topic by Saint Wenhao: Optional Hourglass is now deployed
Script:
OP_SWAP
OP_SIZE
OP_DUP OP_ADD OP_DUP OP_ADD
OP_CHECKSEQUENCEVERIFY OP_DROP
OP_SWAP
OP_CODESEPARATOR
OP_DUP OP_HASH160 <pubkeyHash> OP_EQUALVERIFY OP_CHECKSIG
If enough people will upgrade, and if coins will be moved from such addresses, and to such addresses, then only short exposure attacks will be dangerous. And Proof of Work can be checked on every signature in a soft-fork way, so that coins can be timelocked for shorter or longer amount of blocks, depending on how small a given signature is.