Some grey zone of 1 and 2.
With the addition that there will probably be some new angle on the whole thing. Probably more presumption of computer involvement. I'm not at all saying "4E is too computer gamey and 5E will go even farther". I'm saying that the assumption of computer tools at hand will only grow and impact overall society and D&D will just be along for that ride. No specific details on my prediction, just a general expectation. (8E will involve 3D virtual reality though
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As much as I love 3E, I'm the first to admit that it has well and fully run its course economically. My negative attitude toward 4E has nothing to do with 3E neogrognardism. I was pumped about a new edition and ready to move on. It was the details of 4E itself that turned me off.
The reason I say that is to point out that as a HUGE 3E fan, I was really ready to move on when 4E was announced. 4E was announced in August 2007. That is only seven years after 3E was released.
And 3E had 3.5 helping it along. There is no question that 3.5 was a kick in the teeth to the 3PPs. But WotC was able to push a reset button and recycle a ton of product titles. It extended the economic viability of 3E for WotC themselves.
So we have around seven years of life. Some time before that WotC had decided it was time to start over, and another year after that before 4E was ready to hit shelves. So the life is in the 6 to 8 year range. Call it 8, because that is how long it takes to birth the replacement.
WotC has promised that 4.5 won't happen. Now, they could certainly see the hand writing on the wall and change their mind. And that would undermine my thinking. But for now I will assume they keep that promise. That takes the reset button out.
Also, one of the big points that 4E fans praise about it is its appeal to a wider fan base. I accept that. I just believe that is a short term plan. Since D&D first saw light, there have been gamers and non-gamers. Shades of grey certainly. But we all know that the distinctions exist. Being a non-gamer does not mean you won't play D&D. But you are not going to be somebody who buys a lot of product. 4E has tapped into a lot more of these people than any prior edition. And 4E has lost some hard core gamers as a trade off. But, probably a very solid net plus in terms of total headcount. The problem is, the non-gamers are going to move on. They are not going to wake up one morning and decide they need to flee this geek thing they find themselves enjoying. They will just find that other things will come along. It much more a fad than a hobby.
Of course there are always new gamers coming along all the time. And the current version of D&D is very likely to be the first stop for these people as well. These will be true "new gamers" that start with 4E. Many of them will be 4E gamers. But many of them will move on to something that is more gamer targeted rather than staying with the casual based 4E.
So you have 6 to 8 years, minus reset button, minus fad support factor.
To brush on edition war, I also believe that even a lot of gamer fans will find that the homogenization and simplification will result in faster burn out. That doesn't mean you are not loving it now. But ask around. A lot of people who loved 3E are done. It happens. It will happen again. I just strongly believe it will happen (is happening) faster.
The 6 to 8 year window is a very optimistic target.
But they are not going to leave D&D. Everything is for sale. And they could dump it if the right offer came along. And the right offer may be less in the near future than it is now. But D&D isn't going away.
But right now the wheel is spinning faster.