Grass won't be growing all that well rolled out in November in December. no, but summer/spring/fall months it would grow well and still allow the Bears to use the stadium for other purposes, march madness, concerts, what have you, and not destroy the turf doing so. Plus, a grow-house could be constructed next to the stadium if you want to keep it warm but dormant during the winter That's true I guess. Lambeau uses some sort of artificial light growing system for the winter months and they do pretty well. They also have that hybrid grass that's reinforced with turf. If it works for them I'd think it works for Chicago and then you just gotta put the whole field on giant wheels (basically). As far as other venues, this is just my wacky idea with zero professional knowledge. Grass as your base level with optimized NFL sight lines. An artifical light/irrigation system that rolls out over it but that can also support weight of your secondary venue floor like NCAA tourney. You raise the floor a bunch, but those bottom row sight lines are useless anyways for stuff like that. So while the Final 4 is rocking above the grass you have lights and irrigation keeping the grass happy underneath. I guess it's a question of strength if that support system being possible? I remember reading about Vegas's structure and they had a similar conundrum because they wanted to maximize seats. Whereas Arizona kept the rollover section as lean as possible, Vegas had to really beef up engineering to hold seats and allow the field to roll under. Then for Tottenham they took the approach of splitting the field. But that seems like a worse option for NFL. Otherwise I guess yea, you do the exact same design (basically) as Vegas but in your empty field have some system to erect temporary green structure and artificial lights for Nov-Feb growing. In either form, probably using Lambeaus hybrid turf is best bet.