I feel it would depend on how they make it. Like X-2, then perhaps it's not such a good idea. Gameplay and story would be a major factor, especially since there is very little left in Spira for a further extension to the Tidus/Yuna story arc, perhaps if it was set in a completely different time, new places in addition to the old, and new characters, then it might not be so bad...

Slightly off topic, but I feel relevant, what's your stance on the VII spin-offs?