It is more nasal and I am not exactly sure why. Age sometimes deepens the voice, which often adds a really nice richness to compensate for the loss of range. Phil's voice has changed in tone in multiple ways over time. It was lighter and initially lacked heft early on, then became stronger and lost some of that light touch, it then became warmer, and then became lighter and a bit more nasally as you mention.
There are a number of songs that might fit his voice now. Some would be great to hear - e.g., Blood On the Rooftops, Inside and Out, the full Cinema Show (the high bits are falsetto). We'll have to see what the final setlist looks like.
I guess the only thing that stays consistent in life is change. He’ll compensate for his voice change. Thinking of artists who’s voices have aged gracefully, I love the way Robert Plant sounds now. He’s got this richness to his voice, almost like a soulfulness. His last solo album was wonderful, IMO.