The 1.8T is paired with the IS12 turbo, which is the smallest of the turbo options on the EA888 Gen 3 engines. A Stage 1 remap will improve torque and hp to an extent, but you will not be getting the top end power the S3 will have with the IS38 turbo. That being said, the IS12 is quick to spool and build boost, which makes the car very drivable in day to day use.
An option is to swap in an IS20 turbo, coupled with a tune. This will give you better performance, and closer to a stock S3 territory. I would hesitate to drop in an IS38, as it will be slower to spool in day to day driving.
