However, none of **=, +=, *=, &=, <<=, -=, /=, |=, >>=, .=, %=, ^=, //= and x= would be useful for arrays.

Actually, x= would be:

$ perl -we '@bar = (42, 5); (@bar) = (@bar) x 5; warn "(@bar)";'
(42 5 42 5 42 5 42 5 42 5) at -e line 1.
$ perl -we '@bar = (42, 5); (@bar) x= 5; warn "(@bar)";'
Can't modify array dereference in repeat (x) at -e line 1, near "5;"
Execution of -e aborted due to compilation errors.
$
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