I thought this question has been answered here before, and that the answer went into some detail about why this is done from time to time, but I can't find any trace of that now.
The epoch could, technically, potentially, be in the past or the future by quite a lot, as long as the satellite isn't falling too quickly, since the SGP4 algorithm propagation is predictable and deterministic.
In other words, the epoch could be next year, as long as when you run a recent, supported SPG4 propagator it produces a fairly accurate answer now. However, most people interpret the epoch as the time of best accuracy, though it doesn't necessarily have to be.
So I think the answer to the limited question
Can the TLE epoch be listed as in the future?
is yes it could be. Nothing mathematically prevents that from happening as long as at the current epoch (i.e. now) SPG4 returns a fairly accurate answer that hasn't burned up in the Earth's atmosphere yet, and this is because SPG4 is predictable and deterministic.
update: I went to Space-Track.org and downloaded all TLEs issued on day numbers 191 and 192 of 2018. You can see there are many issued with epochs days or (not shown) months in the past, and some stragglers with epochs many days into the future. That the TLEs with epochs in the future are higher altitude is probably meaningful. Plotted with https://pastebin.com/LaxR6p4Y