At the moment shroud regens 1060 (or something very very similar) mana at level 50.
It does not scale with PIE.
I don't really want to bring class comparisons into this, but Aetherflow regens 20% IIRC.
The current mechanic of shroud is also detrimental to any PIE builds, which I guess is fine since stats have downsides. Whilst PIE does have other uses such as the 2% regen, mana usage - for the most part - is controllable in current content (Coil 1-5).
My suggestion is that shroud should have a partial PIE scaling component at the bare minimum. This is suggestion is not because WHMs need to regen more mana, but that in the future this will make PIE a worthless stat (it's actually pretty bad already).
The purpose is not to buff/nerf shroud, that doesn't matter. It's to give shroud a PIE scaling component so it remains useful throughout, essentially, all content and tier levels.