Just a thought, if we have to make our application cross-platform, then is it possible to create a cross-application OS?
Technically yes as long as you limit the scope of all to all applications that run on major OSes.
It is theoretically possible to create an OS that could handle applications run on the 4-5 most common OSes but the amount of work involved would be monumental.
Every time a new feature was added to any of the OSes, you'd need to add it to your OS too - So as well as being almost impossible to build, you'd need a large enough dev team to stay ahead of 4-5 of the largest dev teams/groups in the world.