If Satoshi didn't intend for anything like this to be added, he wouldn't have had a reason to implement a scripting engine in the first place. Transactions would just have "inputs" and "outputs" and nothing more.
He wouldn't have included NOP1 through NOP10, either.
I file this under "Satoshi is a genius, part 9,432". It gives a smooth upgrade path using the same blockchain if ECDSA or SHA256 start to get fragile.
Attacking old clients by sending them coins with "will-never-be-satisfied-but-they-can't-tell-that" inputs is a concern-- it is basically the Finney attack, but anybody will be able to try to pull it off and there is no time constraint.
However, I think the benefits of being able to send to a truly secure address FAR outweigh the risks, I don't think it will be difficult to get people to upgrade to a newer, more secure client, and accepting 0- or 1-confirmation transactions is always a bad idea.
I also think you're exaggerating the impact-- OP_EVAL does not invalidate all of the security review that has been done so far, especially if the scripting language being EVAL'ed is unchanged from what we have today.
(PS: the latest git-head QT bitcoin contains a working bitcoin URI handler)