Well, maybe we won't find anything akin to electricity again; the electroweak force is one of the three fundamental interactions we know affect matter in the universe, and knowledge of electricity as such dates back at least to Plato, 2500 years ago. It was unified with magnetism in 01873, and unified with the weak force in the 01970s. Maybe we'll find a fourth one; maybe we won't. (Gravitational waves weren't observed until 02015, and they solved the mystery of short gamma-ray bursts in 02017.) Here's a list of candidates for similarly fundamental discoveries:

1. Maybe we'll find a fourth fundamental force that we just haven't noticed yet. This sounds stupid until you realize that we hadn't noticed Archaea until 01977 or dark matter (85% of matter in the universe) until 01980 (though the phrase is from the 01930s), and we still know almost nothing about the behavior of dark energy, the existence of which wasn't known until 01992.

2. Maybe we'll find a way to reconcile general relativity with quantum mechanics ("quantum gravity").

3. Maybe quantum computers won't work, demonstrating a flaw in the assumptions of quantum theory in the same way that the Michelson-Morley failure to detect an ether wind demonstrated the flaw in the assumptions of Newtonian physics that Einstein resolved with special relativity. More likely, they will work, and this will change a lot of things; their computational power is still poorly understood. They were originally proposed (by Feynman) as an engine for simulating quantum physics.

4. Maybe dark matter and dark energy don't involve a fourth fundamental force like the strong force, gravity, or the electroweak force, but we still know almost nothing about how they behave. So almost everything about them is unknown. Can we use them for communication, propulsion, computation, energy sources, mass sources, etc.?

5. General relativity hasn't been shown to conserve energy or (equivalently) momentum. Does that mean reactionless drives and perpetual-motion machines are possible, or (more likely) that there's a more subtle symmetry to GR that hasn't yet been discovered?

6. Where does consciousness come from? It's the most perceptually salient phenomenon in the entire universe, but we don't have any convincing account of what it is.

7. We know very little about plasma dynamics. We don't know how to make a usable plasmoid gun, we don't know how ball lightning works (or even if it belongs in this item), and although we know they're a magnetohydrodynamic phenomenon, we don't know how solar prominences are formed, and similarly for solar flares, which accelerate some particles to GeV speeds by means we don't understand at all. We don't know why the solar cycle happens. Coronal waves weren't discovered until 01995. We don't know how to stabilize fusion plasma in a tokamak. We don't know if there are significant magnetohydrodynamic phenomena at scales larger than a star, much less larger than a galaxy. We don't know what heats the corona. This is important because a large majority of the matter in the universe is plasma, and our understanding of it is mostly just empirical, like stamp collecting. We're used to thinking of plasma as an undifferentiated homogeneous continuum like a well-mixed liquid, where nothing interesting happens, quite unlike all our complicated organic molecules (which can't survive in it), but obviously from looking at the sun that isn't the case; we really have no idea about the possible complexities. Is this where the Hercules-Corona Borealis Great Wall comes from? Perhaps more excitingly, if MHD makes stable structures possible in large-scale plasma systems (as it evidently does in the sun), are there analogous phenomena that can occur in a quark-gluon plasma?

8. Forget about magnetohydrodynamics for a moment. We don't even understand regular hydrodynamics. Tao's most famous result (02014) was a finite-time blowup in a version of the Navier-Stokes equation, for which he had to use results from automata theory: https://terrytao.wordpress.com/2014/02/04/finite-time-blowup.... What this means in practice remains unclear (Tao: "In principle, it might even be possible in this case that the speed and the wave number both go to infinity in finite time, a scenario known as finite-time blow-up. Of course, such blow-up does not mean that a physical fluid such as water can exhibit this behaviour, but it does mean that the Navier–Stokes equations cease to be an accurate model for such a fluid in these cases."), but it's clear, if Tao's result can be extended to the real Navier-Stokes equations, that it means we don't have an adequate model for fluids in such cases.

9. Okay, and what's up with the profusion of apparently random physical constants? Could they have been different? Are they different elsewhere in the universe?

10. How did the universe start out with such low entropy? Equivalently (or possibly not, depending on the nature of CP violation), why is the past different from the future?

11. Is spacetime continuous, or is it like a sort of foam? Is the foam size really of the Planck-length scale, or is it much larger, as the holographic principle suggests? What happens when you approach that scale? Fundamental particles like protons are far too big to do experiments like this, but in theory we ought to be able to make black holes that are much, much smaller than protons to do these experiments. (You think NIMBY is bad now...)

12. String theory posits a number of other spatial dimensions. Is spacetime really only four-dimensional?

Quite aside from these fundamental problems, any one of which promises a "largely unexplored field of science akin to the discovery of electricity", there are a huge number of things we can create that don't even require discoveries of fundamental new phenomena like those above. Electrochemistry, to take one of your examples, is extremely underexploited because in most cases we don't know what conditions we have to control in order to make our experiments reproducible, and of course medicine is full of unknowns.

Of course anything could happen in future generations, but there's nothing to suggest that your prediction will happen. Rather the other extreme: the well of discoveries is overflowing today, but may become a geyser in future generations.