Only parts of it aren't enabled. You can already do a lot with Script:

"This is a list of all Script words (commands/functions). Some of the more complicated opcodes are disabled out of concern that the client might have a bug in their implementation; if a transaction using such an opcode were to be included in the chain any fix would risk forking the chain."

https://en.bitcoin.it/wiki/Script

What are you talking about? Every single transaction uses the bitcoin scripting language, and has since the genesis block. There are certain rules about which transactions are relayed based on the scripts they contain, but scripting certainly is an integral part of bitcoin as it exists today.

Custom scripts aren't run. At this point, scripts are just exceptionally long identifiers for predetermined actions.

Simply wrong. I suggest you actually look at the source code to bitcoind (start with script.cpp, and the validation methods in main.cpp/core.cpp which call it).

My mistake. I was under the impression the whitelist was quite restrictive, but maybe not.

Thats not correct. They're executed, and fancy scripts are sometimes used on the network.

Common wallet software just uses templates to create and decide which scripts are relevant to them— but the network itself absolutely does validate them.