I'm honestly surprised. Cautious too perhaps, but as it's a completely different setting/cosmology, less than I otherwise would have been.
Will be interesting to see if they try to present them as a reintegration of the Sons of Mercy and the Sodkillers, or if they ignore the Faction War splintering of the Faction into its original two founding factions that were independant prior to the Great Upheaval. Given that any take will be a new setting, they won't necessarily be using any of the prior history of Sigil, so color me interested in seeing how faithful to its roots they are.
And yes, I will drool over art of Alisohn Nilesia if they present her as Factol. I'll give them a week's pass on 4e criticism if they depict her in some capacity in some artwork. Insane, justice obsessed tieflings are awesome.