yes, you're right, increasing the playback speed would be a nice feature. I tried to tackle the problem when we first introduced the explorer but it turned out to be not as easy as simply showing data "faster". At least not with the current API design.
Currently the explorer requests new data every 5 seconds, animating aircraft in between. Data is always retrieved for the whole network, because a lot of explorer features depend on having all data available. For example, searching through all live aircraft is client side only. These features would break if only a small sample of the data (e.g. the currently visible area) would be requested.
So increasing the playback speed would essentially mean something like bringing down the 5 second interval to a 1 second interval (1 data point each second), requesting data for the whole network once each second to get a small playback speedup of only 5x. However, requesting historical data can quickly get a lot slower than 1 second (grabbing the data + transmission time can easily be ~5s or more, depending on how old the requested data is). So simply requesting the same data faster is not feasible.
Another option would be to leave the 5s request interval as it is and to decrease the sampling rate (e.g. requesting data of every 25s to get a speedup of 5). However the animation barely works well with the live sampling rate of 1 point each 5s in cases where aircraft change their heading. Lowering the sampling rate even further would break the animation.
Of course there are ways to implement a playback speedup, but they all require fundamental changes in the frontend as well as the backend and therefore the feature will probably not come anytime soon.