> Not to mention that the search space is massively massively larger
That's what I'm not really convinced about. The build-order space is not that big (compared to Go's positions) and once you got a good micro-management engine I'm affraid this will lead to something like : if protos or zerg pick protoss then 8 gate -> 9 pylon -> scout : if no counter to 4-gates, then 4-gates and win from out-microing.
The preferred opening for Protoss in PvZ (on most maps) is the forge fast-expand. If the Zerg player doesn't want to play an economic game in response, they have a variety of all-in strategies available. There is a lengthy article on Team Liquid about how Protoss should respond to these.
2. Good scouting is required for most of these situations.
3. There are terrain-based considerations all over the place.
4. There are considerations based on how many units were lost in earlier engagements all over the place.
Enumerating all the build orders (#1) is pretty easy (as you said, build order space isn't that big), but the interaction between terrain and building placement (#3) is a lot more complex and starts to interact with the full game's massive search space more, and the followups are dynamic (#2, #4) so I don't think the game will degenerate into a solved solution as long as it looks anything like regular play.
It's possible that there's some degenerate micro-based solution that turns everything on its head, of course. Bot-based vulture micro might rewrite part of the Terran matchups, but it doesn't seem insurmountable yet. My own bot gets units across the map 5% to 10% faster than normal, but that doesn't look like enough to break the game even with a 4pool.
> Not to mention that the search space is massively massively larger
That's what I'm not really convinced about. The build-order space is not that big (compared to Go's positions) and once you got a good micro-management engine I'm affraid this will lead to something like : if protos or zerg pick protoss then 8 gate -> 9 pylon -> scout : if no counter to 4-gates, then 4-gates and win from out-microing.