If you could control gravity or inertial forces, you would have a propulsion breakthrough (thrusting without rockets), a means to create synthetic gravity environments for space crews, a means to create zero-gravity environment on Earth - hey that could be fun - and a whole host of other things.
Like "Warp Drives", this subject is also at the level of speculation, with some facets edging into the realm of science. We are at the point where we know what we do know and know what we don’t, and there is a lot that we don’t know. The better news is that there is no science that says that gravity control is impossible.
First, we do know that gravity and electromagnetism are linked phenomena. We are quite adept at controlling electromagnetic phenomena, so one can presume that such a connection might eventually lead to using our control of electromagnetism to control gravity. General Relativity, another one of Einstein’s doings, is one way to describe such connections. Another way is through new theories from quantum mechanics that link gravity and inertia to something called "vacuum fluctuations."
Is this subject being studied?
Historically, gravity has been studied in the general sense, but not very much from the point of view of seeking propulsion breakthroughs. With the newly formed NASA Breakthrough Propulsion Physics program, that situation is changing.