In my opinion it would be really complicated to introduce time travel in the series (if we're talking about it being serious/canon of course). The only way I see it working to it's full potential and without creating major plot-holes and lore-breaking situations would be if it was settled in...
I think I'm a little late for this thread :P
I like to think that as a finished product it would have worked as a sequel better than FONV and (waaaaay) better than FO3. And the concept/idea wasn't bad. The "atmosphere" that it transmited, what was playable, wasn't very Fallout-ish to me: it felt...