I don't think I need to explain that statement but if you really don't know why I said that, here we go:
Beth (yes, I'm abreviating that name because I always place the s wrong, so what?) bought the license. Right? Right.
Beth has no relation to Fallout whatsoever, they have not a single person on board who even ever got close to Fallout during its development stages and they certainly didn't have any charity reasons to buy it because the majority of fans wanted TROIKA to have the license (and Beth did not make any moves that imply they would follow that wish -- buying the license with more money than Troika can afford is a pretty good signal Beth wants to keep the license, no?).
Because they apparently do not want to SELL the license, the only choices are locking it up and waiting until nobody wants another Fallout title anymore or beginning the development of a new title using the very license you bought.
Now usually you don't buy things you have no use for. Unless Beth's management consists of the target audience of home shopping tv channels, they would not buy things that sound good but will not have any present use. Read that again: I base this argument on the idea that Beth's management people have fully working common sense, that alone is more respect than most people I know want to pay to them, so don't think I'm being hard here.
That means if you want a franchise, you will know what it could be used for (i.e. what game to make out of it) beforehand, especially if you are going to pay a lot of money for it. Unless I'm more fucked up than I know, that is considered common sense.
Now, it is understandable that the auction of the Fallout franchise might have come unexpected and that Beth didn't have the time to get any devs find anything they could use it for except for holding onto it and grin, but even then you would expect that they at least had SOMEONE who had SOMETHING even REMOTELY SIMILAR to an idea as to what they could use the franchise for.
So now let's expect Beth to have had enough sense to have some guy have an idea for such a use at the time they spent a lot of money to get the franchise. Unless said person bailed or died spontaneously (of heartattack from the excitement of having the franchise maybe?) said person will have worked on a design document since that very moment. Again, I am basing this on the idea that Beth's management follows common sense.
Now certain things are basics, they are the framework for a game concept. Such things are whether the game should be Fallout canon or not, whether it should be fast paced action or traditional roleplay, whether it should have a traditional PCRPG interface or play like a console RPG, whether it should be First Person focussed or have the player be a spectator. Things like these (and the ones I listed are mostly of technical nature -- there are a lot more factors for gameplay) need to be decided before the game's storyline, setting, interfaces and graphics can be developed. Note that I'm only talking about concepts, not renderings or tech demos.
Game designs don't appear out of the blue, first you develop the frame, then you fill in the details and maybe readjust the frame slightly(!) so it can make a good final game. Once the framework stands and the first rough concepts are added, production can begin -- since most modern games are on tight schedule production might begin way before the last details are clear, but even in traditional game development the details might change throughout the production (from what I've read in the Fallout Bible Fallout's design doc at the initial production stages might have been very different from the same document at the time the game went Gold).
Now let's take a look at Fallout 3. Fallout 3 is in pre-production. That means it is being developed but not in production yet. However Pete tells us that there are no developers. If there are no developers, Fallout 3 is NOT being developed. If Fallout 3 is not being developed there is no concept for Fallout 3 and nobody is putting any thought into it. If people are working on ideas and concepts, it is in development and these people are developers. Common sense, simple logic.
Well, then again. Maybe I am wrong and Beth does NOT follow common sense.