I've recently bought my new A4 S-Line 2013 (B8.5?). Never owned an Audi before and it's a great car, low mileage and drives great.

It's the 2L 140bhp but I plan to get it remapped as apparently 185bhp is achievable, has anybody else had theirs remapped?

I've been reading about the MMI and currently have the Concert system (This one) installed and thought about upgrading to the 2G or 3G, from what I can see the price range is from about £300 ~ 600 (excluding installation). But if you had all the gear is it a straight swap?

It can be done but as you've pointed out it's very costly. It'll all have to be coded to the car too 

Yes it seems the difficult option, especially since you can get RSNav system for around the same price. Seems much easier to fit also.

Yea, it's definitely worth looking into 👍