3. Really hard to pull off. We do have RPR though.
Nah just look at SMN, it plays a lot like a Shapeshifter would imo. The main difference I would make would be to have the forms interact with each other so rather than cycling through them at an even pace you bounce around between forms more depending on what you need at the time.

This assuming the job has multiple forms to choose between rather than a base form and powered up form which would be a lot more like RPR though a Shapeshifter imo would make much more use out of its powered up form than RPR does Shroud, like 50% uptime minimum.

A wizard who uses sigils, ritual circles, runic symbols and/or ancient writings that then trigger spells.
You can make it dark and sinister, something along the lines of a master of ceremonies, with blood sacrifices, demon portals summoned from pentagrams and temporary demonic servants who are briefly humiliated to do so, and a forgotten evil script from a book written in blood.
You can also make it more neutral a spellcaster, for example, or more classic direction runescribe.
The important thing with this class is that it doesn't cast spells directly itself, but it all runs through these sigil spells, and writing/symbols. So it will feel absolutely different from a caster. You sort of call upon powers and focus this on sigils on the ground, or characters written in the air and then you bring the magic to life with that first.

So it's a caster that plays a little slower, prepares over these anchor symbols/writing/banning circles and then the powers he calls then do their job, or the effects are triggered. A seal circle provides protection, or the ritualist creates a circle of soul sucking and when 3 mobs die in it, it splits the ground and a horned demon temporarily gets out impor and fights for the group.
That's a good place to let off steam.
The important thing is to make it clear to the player that he is not a wizard in the classical sense, but it feels absolutely different from direct spellcasting.
Sign me up! Sounds cool and unique, I want to see more of this.