Making the modifications is not enough.  You need to upgrade every bitcoin node in the world as well.  And research suggests that blocks larger than 4 MB would be unsafe, so I doubt you will be able to convince 100% of all bitcoin users to "upgrade" to something entirely untested like that, backed only by some secretive backroom dealings.

Segwit as it is with 4 MB blocks can be deployed in two weeks, however.  There are still thousands of nodes not supporting segwit, but it doesn't matter.  Those will continue to work just fine, since it is a soft fork.