List assigment ({...}={...}) and UpValues

Question

Let's say I want to track any assignment attempt for a variable a:

a /: Set[a, x_] := Print@{a, x}

This works as intended:

a = 5
(* {a,5} *)

a
(* a *)

However, this doesn't catch the {...}={...} syntax:

({a, b} = {1, 2})
(* {1, 2} *)

a
(* 1 *)

And the following obviously does not work:

a /: Set[{___, a, ___}, x_] := Print@{a, x}

TagSetDelayed::tagpos: Tag a in {___, a, ___} = x_ is too deep for an assigned rule to be found.

(* $Failed *)

This leads to the following two questions:

• Is there any way to "nice" way to achieve such functionality? (By "nice" I mean something similar to assigning the definition to the upvalues of a, as opposed to e.g. Unprotecting List/Set and attaching the definition there)
• Why does Set not simply "thread" over the lists to give upvalue definitions a chance to catch the assignment? As it stands, this potentially breaks many "smart" symbols (e.g. file backed symbols) if the user ever decides to use the list assignment syntax. Is there anything what would not work if this would be the case?