What frightens me is that there is no way back if we make this step and it turns out to be a wrong direction.
Please explain to me how ANY of the proposals (the original OP_EVAL, BIP 16, and BIP 17) are any different in the "what if we change our minds and want to remove support" case?Removing support for BIP 17 would be harder than removing support for BIP 16, because if the network doesn't support it all BIP 17 transactions can be stolen as soon as they're broadcast.
Imagine there are a bunch of un-redeemed BIP 17 transactions in the block chain and support for BIP 17 goes away. Every single one of them could be immediately redeemed by anybody.
The situation is better with BIP 16, because of the "half validation" done by old nodes. Admittedly not a lot better, but it is the "belt and suspenders" nature of BIP 16 that makes me prefer it.