Well, back in the late 70s visual effects pioneer Douglas Trumbull envisioned the film "Brainstorm" to be a traditional 24fps film that would switch to a larger format, 60fps playback for the shots that are viewed through the device (ie Showscan). Ultimately there were huge technological hurdles to overcome and pretty much no theater owner back then would put up the money to upgrade their systems for just a single movie (back then most were mom & pop privately owned theaters, not the vertical monopoly you see today with chains owned by the movie studios themselves). Things are quite different now and in fact modern digital projectors you find in the average theater are capable of playing back anywhere from 96 to 144fps. But the actual workflow of film production at higher frame rates was a major tech hurdle that couldn't be reasonably dealt with until the move from optical film to digital.
But more to your point, 48fps doesn't require us on the post-production side to really up our game so much as it just requires us to generate a LOT more data and generally take longer to do certain things. It's actually 3D that is our biggest headache at the moment, preventing us from using any number of tricks to make things look good because whatever fix we do has to work in stereo. For example, something as simple as painting out a splash particle digitally has to be done for both the left and right eye and if you don't do it with meticulous care, people watching the film will notice that
something's just not right here. In fact, low budget 3D films suffer from this all over the place, which is why they often give you a headache. On something I worked on very recently, there are still problems that couldn't be fixed in time, as much as we tried and a sizeable portion of that blame went to the fact that we were working in stereo, not so much 48fps. I think the move to 4K @ 48fps or higher will in-fact require us to up the bar on certain levels of detail, though we may still be another 5-10 years off from that.
What we do is already dynamic enough and every year requires us to raise the bar to crazy levels above the year before. In years past it was a technological bar. Take a look at CG characters back in the late 90s compared to now. A big reason why they look so much more realistic than they did in the past is because we can do sub-surface scattering of light in the skin, making it look extremely realistic. Characters are also very anatomically driven these days with bone, muscle and skin systems whereas not too long ago they were really just CG surfaces with an invisible internal skeleton where every muscle and flab was faked by hand. The same goes for things like fire, water and smoke. Go back to "Reign of Fire" in 2002 and you'll see some of the first ever CG smoke effects don't with actual fluid simulations vs "dumb" particle systems. These days we're doing extremely complex fluid simulations of increasing scale and detail, generating TBs of data by the minute. But as much as that technological bar rises, since about 2005 it's been a production pace bar. We're now expected to nearly double the amount of work we've done over the previous year...year to year. That's why we often find ourselves working insane hours and going months without a day off. That production bar is the one that's unsustainable, I'm afraid.
Yet it's crazy how far we've come over time but there will always be a demand to do more, faster and cheaper and it's really difficult when every other studio is trying to outmatch you at every turn. Thankfully, this is a highly collaborative industry with everyone showing off the new things they've come up with and sharing them. Some call that bad business, but deep down it's driven by artists and technicians who do it because they love it (most of the time).
Well...that was a bit of ramble