I thought you already knew, - it’s not only a modified theory of relativity rather a theory of everything, - but of pedagogical reasons, it is better to go stepwise forward..
No, it is simply some self-contradictory musing that when asserted even you don't agree with.
As follows...
1.) Bring down the prevailing SR ( and modify SR)
You have yet to show anything that even opposes SR let alone midifies it or might 'bring it down'. Again focus on working out your own notions as opposed to trying to "bring down" others.
2.) Bring down the idea that GR is the cause of gravity
GR is not the cause of gravity it is simply a general application of special relativity which is a modification of Galilean invariance with the speed of light as an upper limit. Matter/Energy is the cause of gravity. What GR does, quite successfully, is to relate that collection of Matter/Energy by the stress energy tensor to the curvature of space time and thus the motion of bodies and the coordinate values of the measurement of events.
3.) Dark matter and black holes mysteries are then automatically solved.
Black holes or dark stars, a star whose gravitational attraction was such that even light could not escape, were originally proposed by Pierre-Simon Laplace in 1796. Long before SR and GR and thus don't depend on either.
Dark matter is a result of the matter we can see by electro-magnetic radiation doesn't agree with the matter calculated by even just Newtonian mechanics in galactic rotation curves.
So nothing is "automatically solved" you're actually going to have to work at these even after and if you can work out your elastic space.
4.) as you see, - last step is to show that Big Bang was not the start of everything, there was something before..- And at this point you have to ask what was that something" and why did it explode?
We have already discussed that last aspect of the theory, I have not much more to add.
Big bounce theories have been around for a longtime. Now with multiverse and M-brane theories also compatible with both SR and GR.
Problem is you've skipped a step (apparently deliberately), the one where you actually, definitively, consistently (internally and externally) and quantitatively work out the properties, relations and mechanics of your elastic space. Time to stop daydreaming and get to work.
ETA:
Sorry it was John Michell in 1783 that first proposed dark stars, Laplace was later.