Dear Joachim,
Quite a bit of both, I think -- but the likelihood of selling enough interchangeable-lens RF digital cameras to get the price under GBP 1000 strikes me (and Zeiss) as slender.
The mount would have to be M -- huge availability -- and the sensor problems for full-frame with such a flange/sensor register are notorious. Remember too that a digital camera demands much more precision from the rangefinder.
I'm not saying it can't or won't be done -- I've been wrong too many times before -- but if you begin by looking at the total number of RF cameras sold, versus SLRs, and assume that 50% of RF users would buy digital (as good an assumption as any), then the R+D costs would have to be amortized over a tiny market where Leica already has a very strong position.
The Voigtländer chassis is basically from a modestly-priced SLR, and cost relatively little to develop. The RD1 has a relatively small sensor; fitting in even a Leica-size sensor would be difficult, and besides, I assume that Leica has an exclusive deal with Kodak on the 18x27 sensor.
The ZI chassis was a much more expensive undertaking, and building a ZI digital for a decent-size sensor would involve a new chassis again.
Add to this the way that M8 prices will come down when the full-frame M9 comes out -- no-one knows when, including potential competitors -- and that Leica has undertaken to support the M8 for 20 years after introduction, and the competition from used M8s would also kick the legs out from under a competitor.
Cheers,
R.