I haven't been following that closely so this maybe completely off target.
In the OP_EVAL
proposal it states that OP_NOP1 will be redefined as OP_EVAL. My question is what happens to scripts that already contain this op code?
For example say I made an output with a scriptPubKey as follows:
OP_DUP OP_HASH160 dd1a6a4549838b5abff214c81e4b2aba7ddd550c OP_NOP1 OP_EQUALVERIFY OP_CHECKSIG
Currently I think this script would validate (and may even pass isStandard()?). But when the new proposal comes in OP_NOP1 will be redefined as OP_EVAL and the script will no longer validate.
If this script was included in the blockchain then validation would fail for new clients during the initial blockchain download.