The one step undo can only work for selected functions, that will have to be defined appropriately, and only for one step back. Lars termed them "irreversible" functions, I think that pretty much hits the nail on the head.
As far as saving the machine state goes, saving and recalling internally has to work, otherwise you would probably not be able to turn the machine back on.
Loading in data from the computer will also work seamlessly, even if Octopus is playing while the data is sent to it. So potentially there is no need to pause.
Data compatibility across OS versions is a major issue that we are just about to address. I cannot make any commitments yet, but it is something that is long overdue and very high on the priority list.