Also, (reading the same webpage I saw the OP_FALSE on) I do see that a number of commands were disabled "for security reasons", so there already are plenty of eyes ensuring that malicious scripts can't crash the blockchain. The disabled commands are described as: 4 commands to split or combine strings, 4 bitwise operations, and 7 commands that multiply or divide numbers.
There's a Solver in the code that matches transactions to only 2 allowed templates/formats. Without passing this template, transactions cannot make it into the memory pool and don't get propagated.
If you wish to make a new tx type you have to lobby for it to be included in the list of templates.