A thread on the WTM forums about skipping the Modern Era and going straight to Ancients so that all kids would be on the same rotation got me thinking. I charted it out, and LemurBoy and LemurGirl are one year off, while LemurGirl and FutureLemurBaby will be on the same rotation... so skipping modern and going straight to Ancients when LB is in 4th grade and LG is in 1st would make a lot of sense.
I like this idea. LB can read Story of the World to LG as part of his work, and they'll get the exposure to eachother's related literature and activities. Eventually, all three will be at the same place at the same time, and LB ends up with a "free" year at the end of high school.
On the other hand... I don't want to skip Modern! It's always been the part of history I've found most interesting, and I have a lot of books I'm looking forward to reading. Also, the period around 4th grade was, for me, the time when issues such as Nazis, concentration camps, and nuclear bombs were big concerns that haunted my thoughts, and it seems to me a natural time to address them.
My thought at the moment is to compromise - introduce the modern era through literature during 3rd, 4th, and 5th grade, while formally studying other eras. My only concern is that LB won't yet be a strong enough reader to handle that all at once.
It's three years down the line. No need to decide now.