Why no compound assignment logical operators?

Evolution Discussion
4

Speaking of short-circuiting, one slightly complicating issue I can think of is the following.

For example, the following two similar snippets are crucially different:

A:

var b = false
b = foo.frobnicate(by: x) || b
b = foo.frobnicate(by: y) || b
b = foo.frobnicate(by: z) || b

B:

var b = false
b = b || foo.frobnicate(by: x)
b = b || foo.frobnicate(by: y)
b = b || foo.frobnicate(by: z)

(A frobnicates foo tree times using b to see if at least one of them returned true, while B doesn't frobnicate foo at all, and is probably a programmer's error. EDIT: Correction, B frobnicates foo at least once, ie until and including the first that returns true, whereas A always frobnicates foo three times, using b to know if at least one of those three mutating calls returned true. TLDR: Both variants are useful, but clearly different.)

But a hypothetical ||=

var b = false
b ||= foo.frobnicate(by: x)
b ||= foo.frobnicate(by: y)
b ||= foo.frobnicate(by: z)

would only be equivalent to one of them, which one?

And which corresponding one would &&= be equivalent to?

Would it be necessary and/or reasonable to have both variants of each operator?
&&= and =&&
||= and =||

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