There have been a number of proposals that would make this more safe to deploy, e.g. using a flag in the coinbase to perform a majority vote of hashpower to decide the height to enable the feature. Someone obviously needs to talk to some of the bigger miners and see if they have other concerns that need to be addressed but I don't see why a hashpower vote isn't sufficient, since the feature is non-forking.
I pulled a Satoshi and decided to implement OP_EVAL to make sure it would actually work.
https://github.com/gavinandresen/bitcoin-git/tree/op_eval
Not ready for pulling, expect rebasing/tweaking/changing. But it is fully working on the testnet.
(example transaction here)
The code puts "OP_EVAL" in the coinbase of generated blocks, so the rest of the network can see how many miners support it.
I gathered contact information for the top ten mining pools last week; when there is rough consensus on the details, I'll contact them to see if they have concerns and/or are willing to support OP_EVAL.
I started writing up BIPs for the various pieces of OP_EVAL, I'll post them soon.