Assuming this is for SourcePawn 2 or whatever it's going to be called, so existing SourceMod plugins will still keep its own language?
In that case I'd go for proposal 1 because it's simple and strict. Provide a helper function to get a copy of the array. Maybe something like this:
PHP Code:
new myArray[] = {1, 2, 3};
new secondArray[];
secondArray = myArray.copyOf();
// copyOf creates a copy of the array and returns the reference to it.
Maybe a better name than copyOf, but I suppose you get my point.
To me, the assignment operator only seems logical to use when you're assigning a
single value (primitive or reference) to a variable. It doesn't seem right to assign a bunch of values at once, it's too magical.