God no. Just No. Temp seats to make it rectangular, means no cover at all for spectators, (remembering it will have to be dismountable basically in a day)
Make the basin for cricket, then do something at the RoF for Football and eggball, even on a progressive basis, one side at a time if necessary
Half arsed, compromise solutions create more problems and are not what we need
Cricket grounds are not designed to provide cover (to the spectators) from the rain, just sunshine (and even that only partially at best). If it starts pissing down, the cricket-watching public leave, to return next day.
Football does not stop just because it starts raining - preferably not on the paying public though. That kind of a solution would simply drive more people in front of telly. In fact I am surprised SKY did not think to sponsor a coverless ground for us as yet.