Back when the debate on open seating vs. assigned seating was going I think I commented on a hybrid type approach.

For instance let people with reserved seats board first, then let others board and the rest of the seats are "open seats." I kind of like the idea but I see a lot of potential issues with it.

Various issues would be pointed out with this:
1. For those who reserve a seat but arrive late, there would be the chance the seat they reserved was taken as an "open seat."
Resolution: flight attendants would go through and mark all reserved seats that were not yet occupied as "reserved" or somehow the computer system would be able to designate which seats were open and which were "reserved" by a light color above the seats or something.

But no use talking much about the other list of "issues and resolutions" to this model I could spend thinking about; the decision has been made to move forward in the way they are moving forward, so that is that.