My two cents.
CA made categorical statements in the past regarding no future resets which lured many of us into spending significant time in the previous beta unlocking commanders and units. Had we been aware that future migration or resets would be taking place I am sure many of us would not have invested that much time in the game, and let's be honest time is the biggest investement you as the player will make in any game.
Now with the issuing of closed alpha keys and quoted battle numbers one would assume CA have some record of player achievement in the prior beta, thus if there was a will to, they could award the player base with a similar level of cumulative XP as they had previously achieved. This could be issued to as a redeemable code to the players Steam Arena address but used on their Wargaming account if the two differ.
From a business perspective I understand why they are not doing this. Creating a schism in the player base for a newly launched title would probably be disastrous as you want as many players in the new games ecosystem as possible to ensure queue times are kept to a minimum. Furthermore we don't know what the financial arrangement is with Wargaming, my guess would be that allowing a swath of the dedicated player base immediate access to high tier units would be a big no no for Wargaming.
So how to appease the masses? Maybe offer up a variety of free premium units once they become available along with a period of premium account access and the unlocking of all commanders for free at the start of the game (this last one should specifically not be monetised for former testers).