Watching this whole story, I can say following.
I saw 2 good candidates - Toryn Green and John Borja.
The first one sings well on high notes I think, his voice is good for "Purple" or "Tiny Music" I think. His vocals are a bit typical modern. Though he sang not badly in Fuel. However it is a question whether his vocals will fit STP sound or not.
The second one is good on low vocals, he would be great but only for "Core". His voice reminds me early Scott because he tries to sound like "gold-era-Scott". His "Wicked Garden" cover is really good and accurate, but I'm afraid on "Purple"/"Tiny Music" he would sound too dry and tough...
Do you agree?
The main problem about all these singers is that they lack flexibility and diversity of Scott's vocals.
But anyway they sing not worse than Scott in his last years or even better - it is fair to say.
And even more important thing is - where the composing talent of Deleos will go? Will they stuck in their 60s/70s nostalgia?