The difference? None of those things were impossible to known science, like tachyons are right now.
much like lasers, solid state electronics, crystallography or to send a self-driven robot to mars 80 years ago... And we are no talking about some exotic fluid created by a sci-fi writer; physics have theorized with tachyons and its properties since the 1960's (
wikipedia dixit)
It's a neutrino observatory. It's got nothing to do with tachyon research.
And X-rays were suddenly discovered when a photographic negative forgotten in a desk became blank without being exposed to light. And has nothing to do with Maxwell's equations.
The neutrino story is just a background to the tachyons technology. It can be neutrinos, it can be string theory, it can be quantum unification or it can be the Voyager 6 sending strange data as it leaves the solar system. You can't predict how the science will be in 2084 and much less how it has evolved. At least in a realistic manner.
And 'tachyon technology' is just a name. I only say that dropping a 'cool technology' a century ahead just because now it's completely impossible its a non-sense. On the other hand, we already had laser, plasma, particles and even sonic technology in previous x-com games. We should 'invent' something new.
That line of thinking is much too easy. We're trying to write a realistic game, and that means things that are impossible to known science are not an option. I'm not going into the details again -- I've had this argument before.
I respect if you don't want to discuss this, but... a 'realistic' game involving a multi-race alien invasion from some star at 600 years-light? :wink: