DCS can't be compared to real life. In this very specific matter, it already fall short since :
We respawn
We have unlimited pilots/planes/planes.
No-one dictate emergencies.
(mostly) No-one cares.
Hence, you can't rely on "real life" things, neither "self-control" from player.
If you want to keep taxiway takeoff, I would really suggest to still implement the taxiway overspeed punishing script, and slave it to a detection trigger : Whenever script detect someone speeding in taxiway - scripts just check if ennemi within ~20miles before going into punishing action.
That's my two cents.