As regards to diesel piston engine design factors, piston speed is high due to the requirement of high compression ratios - i.e longer stroke, and is not in itself an engine life limiter - take a look at the piston speeds on some of the HGV units. The real factor to focus on would be fuel injection control, older mechanical systems produced high detonation pressures on ignition - hence the knock and the need for substantially beefed up and thus heavier pistons etc to take the increased associated forces.
Modern electronically controlled systems have managed to reduce the ignition pressure wave substantially by carefully controlling fuel introduction to the combustion chamber - manageing flame propagation and reducing detonation, the resultant noise and hence reciprocating mass.
Give the automotive boys another ten years with Rudolph's design and we can finally kiss goodbye to petrol as a heat engine fuel.