Yeah the schedule surprises me a little. One of the first things I noticed when it was announced is that there is no room after the two Toronto dates to add another couple of shows, while there is room after both Montreal and Chicago to add four shows each. Your proposal, involving the addition of two dates before the originally announced shows in both Chicago and Toronto, seems plausible but unlikely to me. It raises some questions, i.e. why not announce those earlier shows first, especially when 3 July (the "fourth" Toronto show under your plan) is a Friday and would sell well. The band have occasionally announced extra shows before the date announced first, as I noted, but this seems a bit more systematic than previously.
Then again, thinking about it a little more, maybe they do want to hold back a Friday Toronto show because that would give a fourth date a welcome boost. Put initial shows on slightly less ideal dates and make sure they sell - i.e. to people who'll drop anything to see U2, don't care about day of the week - and then move onto shows on slightly more attractive dates to lure in casuals where all the factors need to align for them to drop the cash. So yeah, I do think your suggestion is plausible and wouldn't be shocked if it happened, but on the same token I won't be expecting it.
Keep in mind after Montreal the band might just be planning a bit of a mid-leg break. That's not abnormal. Recall the break between Vancouver and Chicago on the first leg of 360. So all of these gaps may not be filled in their entirety, even when it seems like space exists for extra shows.