You keep saying that but it's not true. She does that for various character voices, but not all. For instance, as the mom in the corn syrup commercial she wasn't nasal at all.
But Vanessa would be the best of the two as an Update anchor. Hopefully they're going to cast an even better option because, frankly, none of the cast likely to be back would make a great Update anchor.
You're right, it's wishful thinking. Seth will man the desk for at least another two years, I'm sure.
Also, with this year's season finale Seth will break Tina's longevity record, 120 shows to her 119.