We will be able to support it mana wise in 5.4. With the extra spirit, the Plea buff and the HS mana buff I don't think we will need to worry too much about mana. After all, mastery build needlessly spams for shields so it is anything but mana efficient.
Remember too that our mana now scales with haste. The HS change probably counteracts a decent portion of the additional mana from spells now that it has a cooldown reduced by haste.
- - - Updated - - -
Haste is higher hps. Mastery has the benefit of increasing effective health / sniping. It depends what you're going for.