The technology to do load follow at a nuclear plant exists.

If you think about it, "base load" has nothing to do with the power source. Given some period of time, say a day, you are always going to have a certain minimum demand for power generation in a geographic location. Congratulations, you have identified base load.

As the grid becomes more distributed and therefore less centralized, you are going to see base load hitting lower peaks because individual power generation stations will have less aggregate demand. But until society reaches a point where at least part of the day there is zero demand on the grid (fat chance) you will always have base load in some shape or form.