Bitcoin script is purposefully not turing complete-- it's not an accident, in fact it's extremely easy to be accidentally turing complete. Turing completeness provides no value for this application and creates additional risks. Helping someone make a bitcoin clone turing complete is like 'helping' them have an infinite coin supply.
There are plenty of limitation in script that are make it less useful, but lack of turing completeness in the script language is not among them.
This has always been my impression, as well. And as we've seen in the past, opcodes have even been disabled to increase security since they weren't completely secure.
There are some words which existed in very early versions of Bitcoin but were removed out of concern that the client might have a bug in their implementation.
To further quote the Bitcoin Wiki, functionality can also always be added if really needed, through OP_NOPx.
New opcodes can be added by means of a carefully designed and executed softfork using OP_NOP1-OP_NOP10.
So I think we've got the mechanisms that Bitcoin needs, already in place.