Discovering the TOE... Either : won't bring much to engineering problems, just be glad to finish the job. It has always been very rewarding to unify laws (Copernicus/Galileo/Newton unify terrestrial and celestial movements, Faraday/Maxwell unify Electricity and Magnetism, Einstein and new insights into electromagnetism and Weyl attempts to geometerize electromagnetism thus creating the concept of gauge field. The following is very much application of gauge theory : Feynman/Dyson/Tomonaga/Schwinger creating QED as the first QFT and this allowed Yukawa to describe nuclear forces (as a field theory), Gell-Mann/Zweig create QCD in the same framework, and then Glashow/Salaam/Weinberg with Electroweak model. Now, everything is just Yang-Mills and Higgs mechanism = standard model) I was just trying to remind how we came to think that unification is useful.
Or, the other scenario could be : we might hope to do better than just having a very efficient model. We might very well discover new concepts closer to what nature really is. For instance, Penrose came up with twistors by motivating his proposal with geometrical arguments : he says that from the very beginning, the definition of a point in spacetime involves (at least) two light rays, that is we must consider as fundamental the light-cone. This kind of reasoning should lead to a theory whose objects (twistors in this case, but that could be something else) are the mathematical "copy" of reality, not just efficient description. It is also Penrose who says, at some point, we physicists will have to include consciousness in our representations. But "where" is consciousness ? Understanding the collapse of the wavefunction during a measurement, would it be through a technical detour involving strings or LQG, should help understanding this phenomenon. Another topic, closer to usual physicists concerns : LQG proposes that spacetime is quantisized : quanta of length, area, volumes... Carlo Rovelli wrote a book on LQG where he claims we did not fully understood GR revolution. He might very well be right.
As you certainly know, there are many different views on what the TOE should look like. It is difficult to make its own opinion, because Penrose, Hawking, Rovelli/Smolin, Green/Schwarz/Witten/Polshinski/Kaku/B.Green etc wrote books it takes a real while to read, and in the meantime (while you are reading the books) other people came up etc (>_<). In any case though, we should be able to undestand the links between those different views.
I hope the quest for TOE will be rewarding, and I have very few doubts that it will.
