Tachyons are theoretical particles and cannot be equated to existing massed particles.

Not only are tachyons possible, but their existence is necessary for many of the most highly accepted current theories of physics.

Tachyons are imaginary subatomic particles that always travel faster than light.

No not ever.

Depends what you mean by "fringe."

Some PhD's in major institutions are doing research into tachyons.

But it is not considered an area that a LOT of research effort is being or should be done.