(Not too important wall of text, if you don't feel like reading it, skip to "The idea is: "
In pretty much every ZvP I've seen recently (and I think ZvT as well) there is the greater spire / ultralisk cavern starting as well as +3 upgrades (and sometimes even adrenal glands) just as the hive finishes. Also the zergs start to accumulate some bank to go for the brood lords / ultralisks as soon as possible and to get as many as possible of those...
And of course, there is the protoss anti-hive timing (or 2-2-1 anti-hive timing from terran) which oftentimes just straight up kills the zerg. And if not, it does huge damage nevertheless...
As we all know this is because of the massive vulnerability, due to trying to get all the things mentioned above (which of course help you later a lot... but now? not at all)
Zergs try to counteract it with enormous amounts of spine crawlers, which will delay the inevitable push. Sometimes by a large amount, sometimes by a small one. Also, the Spine crawlers are very cost-ineffective againts this push, but they prevent you from dying right away, which is a good thing, right?
This means that you kind of have to have a colossal bank, if you want to go for hive and survive.....
Now, this is pretty much what we all know and hate (love?)
The idea is:
Why not have, instead of one gargantuan window of opportunity to die, several small ones? Why not go for hive sooner? And first get hive upgrades, defend the push with an actual army instead of just playing tower defence / game of buying time with gold, and after defending the push with an army, THEN go for hive units?
I have recently seen a couple of games (at BWC I believe), where the zerg was finishing melee + carapace upgrades about 60 - 100 seconds after protoss got an attack upgrade. The protoss then relied on having zealots with better attack than zerglings' armor, and when it was not the case, the protoss had very little chance of a successful attack. Then he, of course, got +3 attack...what happened afterwards? It was for about five minutes till the zerg actually got +3 armor, resulting in horribly inefficient trades between lings and zealots. This of course had cost him a lot of larvae, minerals (and I believe bases and drones too!)
What if he, instead, made one less infestor and went straight for the hive after finishing his infestation pit? And then continuing upgrades on zerglings but NOT going for hive units (and not banking a lot of resources in order to go for them)? He would have traded much more cost-efficiently after the +3 would be finished (which would be about two minutes after the +3 of protoss... but remember, protoss would have +3 attack and zerg would have +3 attack AND +3 armor!)
Maybe he would even be able to bait an anti-hive timing attack, if he e.g. sniped the observer after it would have seen the hive morphing (the protoss would have thought that he is really vulnerable right now, but he would not see the hive finishing, so he would assume that you have started morphing greater spire / ultralisk cavern, but that would not be true)... I'm not saying that the upgrades would be on time for this timing attack. No, what I'm saying is that the zerg would be building army instead of banking resources. And after the (hopefully) failed attack, he would have already a nicely upgraded army AND the possibility of going for hive-tech-units. Also, note that the attack would be much weaker than it usually is, because of the sooner hive, hence the sooner attack, hence not that much time to gather an army, hence weaker attack. (Also, this army of yours could be used for attacking / counterattacking, unlike spine crawlers...)
And if the attack doesn't come? You can start banking resources, morphing greater spire / ultralisk cavern, just the business as usual, the only difference would be that you would have the upgrades sooner, (maybe larger early/mid-game army, if you were intimidated by your opponent) and probably a bit weaker late-game army. BUT you would be a lot safer against anti-hive timings.
Basically, what I want to ask you is "Is it not better to go for the eventual hive transition more smoothly?"... I aim this generally at ZvP, but it might be applicable to ZvT as well...
Please, share your ideas about this. :-)