No, it is not the same thing. Updating index snapshots requires being able to *re-find* a previously made index entry for the current row. And it has to be done 100% reliably. The worst that happens if an index entry is not found when it should be during a uniqueness check is that the uniqueness constraint is not enforced properly; which is bad but it doesn't lead to internally-inconsistent data structures.
Hmmm... OK Fine... I am leaving this proposal once and for all.
Pretending the problem doesn't exist doesn't make it go away ...