How much tuning possible is there in the new MKV GTI?

Tons, like in all VWs. you may be able to generally drop a bigger turbo in, and get a chip, particularly once the market grows bigger. I could not be surprised it that engine could handle some crazy increase. I mean the 1.8T when it came out only had 150hp, then VW themselves boosted it up to 180hp without any big mods. And you may be able to go well beyond that just with a chip, i.e. 205hp, 215hp, based on your engine codes, or more. I could not be surprised if this was true for the new GTI's also.

I used to work in a VW performance shop when I was younger, and I can tell you VW over engineers all of ther reciprocating parts That means the parts that move in a circle while running. Stock cranks can typically handle twice the hp that is put out by the factory. I knew people who used to get 300hp from a 1.8T engine by putting in a bigger turbo, intercooler, chip and better plumbing. Warning: that was for an A4 1.8TQ. I don't reccommend putting that much HP to front wheel drive, you will wrap your car around a tree

Currently VW is working on a 30th Anniversary GTI with the same 2.0FSI engine that puts out 230HP.