Baldur's Gate : The Sword Coast Chronicles : NWN2 Persistent World

Requirements:

Able to cast 9th level spells.

Spellcraft: 29 ranks

Class: Wizard/Sorceror/Druid/Red Wizard/Arcane Scholar of Candlekeep

Duration: 1 Minute/Caster level

School: Transmutation

Benefit: You can cast the spell Epic Shapechange once per day.

The forms that are selectable come from the standard Shapechange list, as well as the list of all Summonable creatures from the spell Epic Gate, as well as the Druid's Magical Beast Wildshape feat.

I would've put the selections more along the lines of shapes that are otherwise unavailable.

Balor, Pit-fiend, Solar etc.

Altho' solar might be questionable, given we got an entire 10-level class for that particular form.
Granted, the Solar from this spell could be one with set stats, and not augmentable via the Wisdom benefits as the Class-specific one does.

Still, I could see Balor and Pit Fiend.
Forms unique to such a spell, which would be why it was picked.
If it just includes forms you can already get from less investment, I think most would pick other feats for optimization. Even with the prospect of "saving a 9th level spell" on something else.

Not to mention, a druid would then just skip Magical Beast shape entirely then. Making the feat redundant.

A druid would have the ability to spellcasting with Natural Spell during Magical Beast Shape, not while using Shapechange.

That is of cause a fair point as well.
Yet, not a mandatory one. Given natural spell is a feat choice (tho 99 percepts of druids most likely take it ).