And I understand your intention
unfortunately there is a serious flaw in doing it like this. Currently you can buy any PvP gear on your main, and with the introduction of Legacy gear it would be very easy to cheat the system. All you would have to do is buy a load of decent PvP gear for an alt, strip the mods and put them into Legacy gear, then send that gear to an alt with little to no Valour.
One fully BM/WH geared alt with little to no Valour tearing through people. So unless they do a major rework on who can buy what and what you can send to alts with Legacy gear, I can't see them ever doing this.