Well, the prop could require replacement as you say and possibly even the gearbox. I don't know the details of the design to that depth but reading form the TC there are two versions of the 2.0 engine, one delivering 99kW and the other at 114kW.
Generally speaking, it doesn't sound like good economics to have two different set-ups using the same gear ratio (1:1.689) for two variants with a relatively low difference in power. But they could claim that.
On the other hand, from a marketing point of view I think they would benefit from upgrading DA40s to the 2.0S version. I'm convinced that would increase acceptance among the sceptics, even if the aircraft are ugly, slow and badly finished at the moment
150+ knots burning 6-7 gal/hr jet fuel isn't too shabby...