I doubt a larger displacement air-cooled (Euro 4 compliant?) engine is going to rev as quick as the 803 so it would be a step in the wrong direction imo.
Ducati found a sweet spot with the Scrambler in mating an engine with amazing powerband with perfect gearing for playfully aggressive b-road riding. It's a proper hooligan/muscle bike without having to resort to triple digit HP claims and pseudo-macho baggage that clings to such.
You can ride it all day between 4-6k RPM and negotiate 99% of traffic commuter demands and people will think "oh, what a nice quiet Sportster you have" or you can ride it from 6-9k with opened airbox and fruity pipe and have people cursing what a menace such activity poses to civil civic-minded conceptual continuity.
If KTM takes the 57HP 300cc 2-Stroke and puts it in a Duke 390 package (weighing 300 lb wet) I will be there, cash in hand