Incorporation of direct injection into a spark-ignition engine offers several advantages including enhanced fuel economy, minimised pumping loss, higher compression ratio, reduced knock tendency and improved transient response. Direct Injection allows precise control over the amount of fuel and injection timing to control performance and drivability.
VW won't have introduced this change on a whim, there is significant focus now on combustion engines environmental performance, particularly if your VW, considering their recent history with the diesel engine scandal.
VW will have done considerable amount of CFD modelling and testing, including long life tests. I would be interested to know what their strategy is for managing carbon build up, I would imagine it is an engineering solution, i.e materials, coatings, injector design, spark ignition, compression, etc. or possibly maintenance but I doubt this.
I would imagine this change will carry across into the Mk8 Golf's, Audi's, and wider VW group cars. I'm not defending the change but I guess we have to trust the VW engineers on this one and hope there won't be a significant long term impact on engine performance.