Assuming MWI of QM, how can we describe / constrain the likely range of existing “worlds”? Assumptions:
This question assumes that we take the Many Worlds Interpretation of quantum mechanics as ontologically true.  I use “worlds” as a description of quantum systems that have decohered to the point where interaction is vanishingly improbable.   Ontological reality is described by Everett’s Universal Wavefunction 
Given this, my question is, how can we describe and/or constrain the likely worlds do/will/might exist?  Any bounding or statements about what is either very likely, or very unlikely, would be interesting to me.  People throw “Many Worlds” around a lot, but never really describe what range of worlds we are asserting.  
For sake of elaboration, here are some possible options I can imagine: 
(apologies if any of these are ridiculous, I’m just trying to lay out  a full range of imaginative options). 
1) Few worlds:   Worlds only decohere rarely when macroscopic circumstances are determined by a quantum level event.  (e.g. World leader decides to start nuclear war based on outcome of quantum-level measurement). 
2) Many similar worlds: Worlds constantly diverge, but most are pretty similar to a human perspective.  (e.g. lots of different worlds where the air molecules are in different states, but it all averages out to stuff that looks the same to me, most of the time).  There are many worlds, but very unlikely a given world we imagine exists, since most are "close" to our current experience.
3) Many chaotic worlds:  Since most macroscopic states might be very sensitive to initial conditions, quantum level differences are constantly diverging worlds into an essentially infinite variation of macroscopic outcomes.  Hitler wins, Trump loses,  somewhere, with high probability. 
4) Most Imaginable Worlds, given physics:  Splitting is so likely that pretty much any world we can imagine probably has/does/will exist, given macroscopic physical laws. 
5) Unimaginable Worlds:  Newtonian physics + concepts such as defined position & momentum only emerge at larger scales (from our perspective). They are not fundamental to ontological reality.  As such, the range of worlds goes far beyond our concepts of physical structures / matter / identity.  Worlds exist out here that might have things like “life”  but operate on physical rules + emergent “structures” that are so foreign, we can’t even imagine them.  
 A: I will precise your question by stating a "point of divergence", as in alternate history (or uchronia) stories. Given a point in space/time, how quickly "macroscopic worlds" emerge. As an example, possible outcome of a given war is different if you start diverging at the beginning of the war or 5 years earlier.  
1/ Few Worlds. Today, online poker sites use quantum number generators to draw cards. So for each cards, there are several quantum measurements actively monitored by a human being and that potentially greatly affect his finance and mood. So even with this strict hypothesis, considering combinatorics, there are gigantic number of worlds diverging quickly every second.
2/ and 3/ Brownian motion shows that a quantum event like capture of gamma ray by an atmospheric air molecule has a macroscopic impact. With chaotic nature of weather and then consequence of weather on word affairs, we are likely in the "Many Chaotic World" scenario. 
However, this doesn't means every possible outcomes of an event is equally likely. Starting from a year before, is it likely there are worlds where Trump loses, but none where Jill Stein win.
4/ From physical laws, starting from a divergence point 4 years ago, you can imagine a world were you have won the presidential election. I don't think that world does exists. 
5/ This may have a meaning if you take a divergence point during the inflation at the beginning of the big-bang. 
