Personally I don't think the principles of special relativity presented by Einstein and co is the full story.
I can easily imagine that no one thinks so. There is a vast world to explore beyond the known frontiers. We may get there one day, or not. This is impossible to predict. This is precisely what makes it exciting (IMO).
I may disagree with this from the perspective of size. Quantum mechanics doesn't say the size or scale that we "must observe it". It happens that "currently" experiments shows that it (quantum mechanics) appears very obvious in the small world. [...]
I do not think what we said is incompatible. Let me explain what I meant.
We have tested quantum mechanics at specific scales and energies up to now. In this regime, we know that it works for sure, and all predictions made from a small set of core principles agree with all data recorded. This of course does not tell us anything about any potentially more fundamental theory, except that this other theory should resemble quantum mechanics in some domain(s).
Now concerning this new theory, there are a few requirements. Does it theory globally do better than quantum mechanics? And there, it is tricky to answer because it is not sufficient to focus on a selected set of observables. We need to consider all of them for which quantum mechanics as something to say, and possibly more (otherwise what is the point of a more fundamental theory if it does not do more?).
In the meantime, there is no way to answer the question about whether quantum mechanics is fundamental or not, as there is a vast domain in which there is just no data points (and in some, not even any theory point). However, it works where it is supposed and known to work. It is already something...
Ook, whatever you say boss.