Quite possibly. As you know by now, the Boston Marathon will be held the day after the Chicago Marathon. The logistics of getting to the expo and picking up the bib for Boston on Sunday are ridiculously unwieldy and risky.
We may find out in the coming weeks that BAA makes some arrangement for people doing the double. But I'm not counting on that. So, the only reasonable way to go about doing this is to fly into Boston early on Friday and immediately go to the expo with my bags to pick up my bib and packet. Upon doing so, and maybe buying the Boston Marathon cap that is my traditional in-person merchandise purchase, immediately return to the airport to catch a flight to Chicago. Even if I can't get to Chicago's expo on Friday, I have plenty of time on Saturday to do so.
Then, immediately after finishing Chicago (hopefully in 3:15 or less), get back to the hotel to shower/change and rush off to the airport. I have always made it a policy to wait until at least the following day to fly out after a marathon, but that is impossible to do in order to run the Boston Marathon on Monday. Hopefully there will be sufficient time available to get to the hotel and drop my bags off, go to the Marathon dinner at city hall (assuming they're going to be holding that, still), and then crash early enough to rest up for the early wake-up to get to the buses and head out for my fourth in-person Boston.
The only differences I would suggest in this plan would be either arriving in Boston earlier or staying overnight Friday (if you want to do more of the expo). However, by staying overnight on Friday, you still risk problems in your travel to Chicago to arrive in time for their expo.
No matter how you slice it, the travel (and stress of it) just may be more tiring than doing this first-ever World Marathon Majors back-to-back double. Good luck!