If you'd have any real world experience about anything, you would give it a chance!
TT can be had with 2.0 TFSI and 3,6 V6 at the moment.
I test drove few weeks ago Audi A5 with the same 3,2 V6 petrol head to head against A5 3.0 TDI. Both were quattros.
The petrol revved higher and sound better. But it doesn't really like to rev, being a big V6 it's more at home at slightly lower revs. This engine is starting to age a bit, it won't take long before it gets replaced with smaller turbo/TSI engines. It isn't a high revving beast, more like a cruiser which likes to keep itself below 6000 rpm.
After petrol, I changed to 3.0 TDI. Turning it on, there was no intrusive diesel-rumbling. Everything was very quiet. You knew it was a diesel but this is far better than previous VAG diesels I've experienced. So far so good.
When driving you note immediately how much more faster the TDI feels. It has more torque and the power is more accessible, it's always there. Despite being some bhp's behing the petrol V6, the diesel actually feels faster!
Needless to say the diesel doesn't rev that high and if you hit the limiter it'll sound pretty muted and boring than the petrol engine. But if you keep it a bit under the limiter oh boy does it fly! It's the best diesel I've ever driven and the manual transmittion it was equipped with felt very natural with it. Usually I prefer an auto-box in a diesel.
This is the first time ever I'd opt for diesel insted of petrol. 3.0 TFSI petrol would be obviously better but as that doesn't (yet) exist, I'd go for the oil-burner.
If the new 2.0 TDI is anything like it's bigger brother, I have no problem imagining under TT's hood. If big coupe A5 feels natural with a big diesel, smaller TT with smaller TT should be just fine.