Everything below relates mostly to the creation of custom maps for tournaments since I don't believe Blizz would implement something like that because it would make the game (even more) harder for newcomers.
We all know what expansions look like in SC2: We have either 8 mineral patches with 2 geysers or 6 gold mineral patches with 2 geysers.
There's no strategical value to the question "which expansion do I take" whatsoever, the "defendability" is simply all that matters. Now in BW there are all kinds of expansions, mineral-only expos, expos where it's sometimes advisable to place the main close(r) to the gas and just mine gas etc. I think SC2 could profit hugely if there were maps with different kinds of expansions.
There's one aspect that I think could really add much strategical depth: geysers. In SC2 we have now 2 geyers instead of one as the "standard" type of expansion. Here I think more differentiated expansions could highly improve the strategic diversity of the game. I could think of the "classic" easy to take and hold mineral only expansions, expansions with just one geyser, but maybe also expansions with even three geysers, kinda like the gold expansions "geyser-wise" (those needed to be ridiculously hard to defend obviously) - scouting those expansions correctly and drawing the right conclusions concerning the strategy of your opponent would imo lead to more exciting games. The decision which expansion to take would become much "harder" in the sense that the player always needed to decide which strategy to pursue because the "type" of expansion would be directly correlated to the units he could produce afterwards.
Also this would add another element of "playing greedy" if you want to call it this way. Right now on most maps it isn't even possible to take the gold right away. Nevertheless I found this always to be something exciting, to see if the zerg gets away with early gold on scrap station for example. If now there were "better and worse" expansions, not only defense-wise but also concerning the "quality", concerning what they yield, this would create a whole new dimension to questions like early aggression vs defensive play.
What do you think, would you like to see something like that in maps too, or does this sound absurd to you?