Speculation is just that, speculation. Mass is an positive scalar magnitude. Think about the speed, it is always positive, but sometimes we put a negative sign on it due to its vectorial nature. Therefore a car running at 100mph to your left is slower than another car running at 100mph to your right due to its negative speed? Also if someone ask you for the square root of 4, have you ever answered -2? Equations are tools, and like any tool, we have to use them properly. Its fun tampering with signs, but maybe there are things more interesting than mass for get a negative sign, time, entropy, temperature (Kelvin scale), space, brightness, wavelength, current, resistors... You can have fun putting in the formulas negative values for this, but not more than fun.
If something is possible it doesn't have to be true.
Something that is true, is always possible. :thinking: