After reading all this, I love the feat. It's pure goodyness to me.
And I'm fine with Infernal Machine. Just as Borka, Barny and Nareesh are with Iron Flesh. Or Xerxis with Inhospitable Ground. Or Constance with Transference. Or Sturm with Watcher. Or Venny with Lamentation. Or Vayl with Purification.
There are no signature spells.