There's likely to be more lower bowl available then you think. I know plenty of people picking relatively early who prefer to sit up top because they like the view better. Now certainly some of the sections are going to go quickly, if your hoping for an aisle seat on the 30 yard half way up in the 1st level and are picking mid June your gonna be SOL. That said if your not overly particular I think you should be able to get a seat in the lower bowl if that's what you really want. Getting a seat next to the tunnel or an aisle seat is probably out if your picking later but the lower bowl itself is gonna have more inventory then you think.
What's unclear at this point if how many people in a section currently want to move within it. That's where the real potential could occur and cause some chaos. If a person in say 127 or 128 who sat in the middle jumps to an aisle seat bumping someone out that can cause a chain reaction that can spill over for weeks. Ditto for someone who is say on the goaline who jumps over to say the 10, those are the real unknowns and why a lot of us donated more to bump up our ranks.