Quarks are now considered to be fundamentals, but so were atoms some time ago. So the way we see is only limited by our technological advances? After watching this FuseSchool - Global Education episode, I cannot stop thinking how can something not have a substructure, how it cannot be split? 
http://www.youtube.com/watch?v=nlv06lSAC7c
 A: You have to realize that all the history related in the video you linked is a short story for the long story of experiments and theories trying to fit experiments, been rejected, new theories explored until the final standard model was solidified into a physics theory. This is a very consistent model that has not been falsified by any experiments to date.
This model is based on a set of elementary point particles that can not be further split non trivially  and still retain the model's validity. By non trivially I mean to make a prediction for an exerimental result that would be different from the simple standard model and if found, falsify it. If this ever happens then to be sure, the standard model will be called "an emergent theory" and the inner levels explored and new theoretical models will be developed.
There exist non mainstream physicists occupied with postulating that the electron or the quarks are composite and experimentalists are looking at all possibilities.

Detectors at the LHC allow scientists to peer even further into the makeup of the smallest bits of matter. It will take many years of data collection and careful analysis to determine if compositeness exists. If it does, its discovery could open up a new world of subatomic particles. The unprecedented energy of proton collisions at the LHC could be what scientists need to find it.

A: Betrand Russell, in fact had mentioned this problem. Of how we would know if we have in fact reached the most fundamental level. The answer is no.  We can never tell for sure. Due in part to the fact of a indivisble object has no unique characteristics or even remotely close to a special property that tells us humans im no longer divisible.  Are inability to know with certainty if we have truly reached the "bottom level" or indivisible particles is for only those with hopes and dreams. therefore there shall allways remain a mystery since fundamental particles have no specialising property to differentiate itself to tell us this in fact is thee "bottom".
Leonardo Bisignaro. 
