Ok take my vw hat off.
The Edition 30 is a limited edition car, not mass produced, it has individually styling, over and above the Gti.
If they change it, it no longer becomes Individual as so will be less sort after.
Vw dont want this, so thats why it wont change, personnally as has been discussed i think it will carry on for a bit or untill the supply out streches demand.
i.e Less people buy and the cars are built and "left on the shelf", they dont want this, at that point it will stop being produced, and then they will switch tooling to the Mark 6.
But dont expect it anytime soon.