I'm confused. Iorveth, no matter what you choose in W2, is important. So, the Roche path is canon. I don't buy it. Even if it is, and I have played both paths, the Iorveth path carries just as much weight and importance as the Roche path. The paths are essentially two separate games and there is no indication that one should take precedence over the other.
Even if we assume that Roche is canon (frankly I see nothing anywhere that says it is, it's all down to the player's preferences) Iorveth is a big character in the game and smaller characters than him have been allowed to make guest appearances in W3. Even characters from the books, that haven't appeared in the previous games.
Some argue that including the Iorveth path would have meant having to add even more alternate stories and outcomes in W3, not to mention a very different start off point. This just shows a lack of imagination.
I can understand that CDPR can't take the already huge W3 and add another start off point based on the existence of Vergen and the non human alliance. However, why not simply slip in information about how the alliance collapsed due to inner strife? Dwarves and Elves don't get along all that well anyway and Dandelion even mentions in his W2 narration that "if not for Henselt's army making camp nearby, the whole rabble would have been at each other's throats in no time".
Then they could have dropped that alternate reality and simply have Iorveth appear in a side quest somewhere, involving Scoia'tael and some delicious morality tale about 'one man's terrorist is another man's freedom fighter' etc. Saskia could be with him, or not. She's a dragon for crying out loud! I'm sure they could have thought of a plausible reason for her withdrawal, at least for the time being. It might have been a bit of a cop out but a lot more satisfying than having some guy mentioning Iorveth in passing, letting you over hear it, if you are lucky. That's so pathetic they might as well have left it out.
Considering CDPR's track record so far, W3 is amazing and I loved the previous games too, I was convinced they were saving Iorveth for a DLC. But now it looks like he will remain simply forgotten, disappointing the many players that choose his half of the W2 game.
CDPR deserves a slap on the wrist for that one.