This skill tree has been missing an ultimate since... well always.
Scribing is a perfect opportunity to give players some more theorycrafting options for some of the staple Buffs and debuffs along with potentially giving more love to some less used buffs and debuffs.

First of all, there should be two new Affix Scripts:
Slayer and Aegis.

In the case of this ultimate, we are of course talking about Major versions of buffs/debuffs.

Other potential Affix candidates for this ulti:
Buffs:
- Force
- Berserk
- Protection
- Toughness (never seen)
Debuffs:
- Enervation (never seen)
- Maim
- Vulnerability
- Mangle (never seen)
- Brittle (1 monster set)
- Uncertainty (never seen)

As you can see from the suggested list above, this also gives PvPers more room for theorycrafting.

The next thing this Ulti could tackle are the class identity issues most players are experiencing nowadays.
By giving players the opportunity to "play the way you want" what they actually got was the same skill lines/skills across all players of the same role. The build diversity in endgame community has really shrunk to the point of total blandness.

One way to try to combat that is to give scribed skills (or ulti in this case) some meaningful Class Signature bonus.

Don't get too hung up on the actual suggested Affix bonuses.
Those are flexible and a thing for the combat dev team to balance.

Is this something that would interest you?