The trouble is, a critical shift will have a major impact on at least one juncture and a lot of the background will become obsolete. Okay, so you'll get some distimed persons left wandering around, but there's still a huge hile that you'd need to write background to fill.

Also, the agents of all the factions are fairly evenly matched against the players. With all the extra Chi that a crit shift might bring they could become unstoppable, which would be no fun to play against.

But having said that, I'm going to have to try and build a crit shift into my campaign now...

I think part of the problem is the way past shifts are often written up. Logically, in the time just after a crit shift it should be fairly easy to restore it, particularly if you were powerful enough to rule a juncture in the first place. However, the way the Monarchs' fall is written up is that they were crit shifted out of power, and were singularly unable to reverse the effect even with their immense resources. True enough, the lack of magic would seriously reduce their power but they could still be powerful enough to try and restore things.

Ultimately it's up to the GM. I think there's too much variability in what would happen if a factio took a juncture for the sourcebooks to sensibly try to evaluate it.

#1: The Pulp Juncture (1935) is open in our campaign. The Ascended run the Juncture, of course, but we posit that during this (and perhaps others as well) period of occult interest, the Ascended build up something of a natural resistance to waxes and wanes in the world's ambient magic field. The Pulp Time is a particularly strong 'wax', and it happens that the 1850s Unspoken Name has taken power again. Interesting note, of course, is that since the Sorcery modifier is positive in 1935, that means it's negative in the Netherworld. Suddenly, detente is broken in the Inner Kingdom and the 1930s Name refuses to give up power _again_. Working from the 1930s juncture, the Pulpers blitzkreiged 1997 with the unlikely aid of the Lotus, Jammers, and the Dragons (who have been on good terms with the Pulpers thus far). They took a chi broadcast tower in Chicago, which promulgated a 2057 Shift. In the new 2057, it's a little more Shadowrun-like, and arcanowave tech is missing completely. Boatman and Bonengel are missing in action. (as a precursor to this, the 2671 Juncture also got taken over by three of the Four Monarchs briefly...)

#2: The Thai Shift. can't talk too much about this one, but for about nine months in game terms, the players have been teased with quick shifts into a Thai-dominant world that suddenly revert back to normal. None of the factions have any clue about this, and everyone's a little panicked about it, as whenever it happens, the reins of power to the world are loosed and no one has access to the chi of their Feng Shui sites. Once the quick shifts stop, power returns to the Innerwalkers with nary a glitch. However, the last switch that happened, stuck. Right now, _no one_ has attunement, and the Secret Warriors are a little worried. I'll be able to talk a little more about this one on Sunday, when some new revelations become apparent (don't know if any of my players read this).

From the background, I gather that the Monarchs actually didn't have much in the way of power or resources at all after the critical shift. Think about it: The 1988 critical shift erased the monarchs magical power and physical resources (their empires, weapons, vehicles, fortresses, etc.); by the shift's very nature of altering history, none of it could have existed. In the new 1988, the Monarchs were nobodies, non-entities. The only resource left to them would be the Innerwalkers under their command before the shift; they'd be the only people who still remembered the Monarchs.

If I remember the background correctly, the key to the Monarchs' downfall was that they didn't pay much attention to the Netherworld; doubtlessly, they would have had some Innerwalkers in their service, but not many at all, as they were too busy squabbling among themselves to bother with other junctures (which is why the 1988 critical shift succeeded). They simply didn't have the manpower, the magical power, or any other sort of power to oust the Ascended from their entrenchment in the top-dog position. The fact that they haven't made any serious attempt to consolidate their power in the Netherworld speaks as much for their continued comparative lack of resources as much as their continued squabbling; the only recent attempt to control the Netherworld, the Molten Heart, was disrupted by the remnants of the Dragons, so they're probably not about to trust each other enough to try again any time soon.

I'd imagine, though, that the Ascended and the Architects of the Flesh, having such a vested interest in the secret war and other junctures, would have a sizeable force of Innerwalkers; enough that they would be able to mount a viable challenge to any critical shift (and, being in the most vulnerable position at the top of the time-line, the Architects would have a plan or six in place for just such an event). The question is, who would the players help?