I'm always fine with new protagonists... UNTIL TRESPASSER.
*FOR ME*, It is not about the pros and cons of using new protagonists, it's about Solas. I'm okay with how Alistair/Morrigan/Other old companion and LI are dealt with in DAI, where we meet them with the inquisitor instead of the old character. Maybe that's because I know the relationship between oldcharacter/LI/companion is settled.
BUT SOLAS? It is clearly that he and inquisitor isn't over yet, and I don't want to watch the two confronting each other, arguing, having all the emotional moments while me the player as a new character just stand aside disconnected. I WANT TO EXPERIENCE SOLAS/INQUISIOR's story in FIRST HAND. I want to know how it ends, through inquisitor's perspective but not from a new character's. This is going to be very personal.
So as long as they can figure out some way to deal with this matter, maybe like temporary playable inquisitor or what, I'm still fine with a new protagonist.