I believe I've heard that there will be a reputation resource at some point, so perhaps this could be something that degrades over time and brings your budget down with it (I also think a periodic budget like this makes more sense than the reward for mission completion like it is in, say, Mission Controller). That way, you'd have to keep launching missions rather than just wait for the next one to complete. One potential problem with this system, and a general one with any time mechanic of this sort, is the difference in time passage between early-game, Kerbin-and-Mun missions and later interplanetary ones. I can get through the early tech tree, send a few orbital missions up and a couple trips to the Mun, then notice that only a few in-game days have passed. My first Duna mission, though, can take up to a year between waiting for intercept windows (and missing them) and travel times. I can't think of a particularly good way to balance that, though maybe just having a spacecraft en route to an intercept could help maintain your reputation (though given that I often have to do mid-course corrections to get myself onto intercept, and everyone probably does for a planet on a different orbital plane, so this presents its own problems--perhaps you could declare a target planet ahead of time, which would give you a reputation boost while it's on the way but a penalty if you fail to reach your target in a certain time). Perhaps, to mitigate the time difference, you would have to design a ship and then wait for it to be constructed, and you could adjust the construction time for a higher or lower cost. I could see how this could get annoying, though, if you're trying to reach intercepts or rescue kerbonauts on a failed mission (though I personally might enjoy the challenge of including emergency escape plans with every mission or having some general-purpose rescue craft waiting either in storage on the ground or in orbit). As to "over time" mechanics like mapping and resource gathering, I don't think that it'd be a big problem to have them working in the background during other missions, though I'm no programmer. I know the "Interstellar" addon has a part that generates science without having to be watched. Mapping might be a little more complicated, but in principle I suppose it should be possible. Even if just this same ambient science-gathering is used, it could make probing more interesting (you could, say, have a part that generates a small amount of data every day that slowly decays until you move the probe a certain distance, making rovers more useful). In the end, there are many possibilities.