Well, sure, if you make the invasion a 100% focus on Daimon Worship, then I think there isn't a way for it to be really fun for most people, to be frank. But though it seems as religion might be put forward in a more important manner this time, I really don't think the plans were to make the invasion 100% about religion, with no invader except for priest invaders.
I'm not saying Daimon Worship doesn't have any potential for fun, either. I'm just saying there are drawbacks and risks associated with it, which are greater the more importance you give to it. These are mostly due to the fact that the only people with a real influence on follower count are priests, which are very few in number and which is a class that has absolutely no appeal to a vast quantity of players (if you consider how many people have never or rarely played a priest).
Not that I think Religion is going to 100% be the focus, but if that was going to be the case, I would suspect that the war would not be over followers in the normal sense. I could see Daimon priest getting special abilities like raising cultist army's etc, and perhaps something along the line of the Light Temples to provide realms a way of countering the religious spread without relying solely on priest. If you think outside of the current priest game, things could be added to either side to provide and interesting religious war.
