I think a logical combination of a speech tree in with a keyword system would be much like how Fallout had it. Except for one major thing, that the topics you can ask them about can lead to, or maybe unforseen consequences. That's something missing in a lot of modern CRPGs. An element of surprise that is believable. Usually "surprises" are scripted into the story, but when you take the "surprises" and make them dependent upon player actions, then it would be a good addition.
They would also have to be well-crafted, because otherwise a dead end would be a reload, unless it gets to an obvious case where the PC would die, resulting in an ending sequence much like the player getting dipped in Fo1 through speech options.
That is a return to the Pick-Your-Path Aadventure books that I feel the style of Fallout's [resentation was based upon in part. Those were early starts of RPGs, too, although more in Adventure. What happened depended upon which page you turned to, but logically through your actions. I feel that speech should be no different than other aspects of the game that could use improvements that fit logically within the design. I believe that this is perhaps the next step for Speech skill systems to take, or at least return to since Fallout did it well. It could be improved on, definitely.
One or the other, at this point, does feel a bit flat. Choosing from a list is a bit corny, as if the actors are remembered in the player's mind, there should be no need to use a list. I liked that in Fo1 where if you thought of something to say to the right person, it might result in something special; now only if that could be expanded upon versus the speech trees that are often constructed poorly or in a cliché manner.
At a tabletop game, a good GDM would hardly railroad the player forcefully without reason into strict speech routines. They can nudge the players, but if the players want to do something, let them feel the consequences, as the old GM rule goes. The players often have to think of what their character would say or want to know about. As Fallout is based in spirit in design from P&P RPGs, I really don't see why this shouldn't be too much to ask. I only state that it be done well, for those who might be reading this.