I have a DVOS and did think ot a waste to have only a c/c filler in that huge body....although it can, of course, be used as an eye-dropper.
A piston-filler seems a good idea, and, as Susanna says, Delta has some experience of making these.
As for the Delta Alfa Romeo pens, I have two red ones: the 1750 LE has a piston-fill which looks similar to the new DV, and works fine, and the Giulietta Trofeo has a c/c system.
I am not too bothered about the filling system, as long as it is reliable, although I prefer the larger capacity of the piston-fillers, versus the versatility ofthe c/c.
I am more interested in appearance, balance, reliability, and, of course, how it
writes 
(All of my Deltas write nicely.)