FPGAs are the best way to preserve a console for the future. The hardware especially for older consoles was very special and custom, basically unique architecture.
While modding the ROMs seems to be easier, it has to be done for every single one and could lead to alteration of the game ifself (timing comes to mind) FPGAs have to only designed once per Console.
FPGAs get more and more accessible and cheaper every day. So for the future it will be way easier, cheaper and more accessible.