Even if your suggested feature might not be breaking (maybe the syntax would need adjustment), I think this still applies here: PSA: Julia is not at that stage of development anymore
What benefit would it bring when this would be added to the language compared to an implementation based on a macro in a pkg that uses the let block trick?
I think the general sentiment is to first try things out in packages (in particular when it needs no changes to the compiler) and then later see if it is worth adding to Base.