You say /s, but COTA might actually be the least difficult to adapt for that purpose. Not that it would be easy in any way, but there’s space to expand the runoff at the new turns 1 and 2, so does the new beginning of the back straight. It would mainly be a matter of money and will, rather than a matter of overcoming impossible circumstances like rebuilding a lage part of the infrastructure of the circuit (which, to be fair, is also a matter of money and will in the end, just orders of magnitude more—a revolution rather than adjustments). Additionaly, there’s the issue of time: you could never, no matter how much money you have, convert Silverstone in the remaining time. With COTA there is, perhaps, enough time.
All this having been said, COTA will, of course, not be converted to be bi-directional. But it could be.