why would a piezo printhead be more ink thirsty than a bubble printhead - isn't ink just a matter of ink volume and coverage on the paper how it looks and which saturation it can acheive ? Nozzle backup is indeed quite a nice feature, but I could imagine that the print speed would slow down significantly when a missing nozzle has to be substituted by another nozzle at another location in the printhead for the same color which would require a separate printpass just for that nozzle. Detecting a missing nozzle is one thing, but the industry has not found a trick to clean individual nozzles yet eliminating most of the waste ink from cleaning cycles. There is not even a cleaning mechanism for an individual nozzle row available in most printers, except for the pigment black in Canon Printers and some Brother printers - cleaning black or all other colors.
Well, that is what I used to think would happen before I thought about it again. If you had enough processing power and finite control within the printer and printhead, you can actually have the remapped clogged nozzle as part of another pass or same pass which was going to happen anyways thereby losing practically no speed. The fast remapping as inclusion of another group is the key. Essentially it requires that the print engine algorithm needs to modify itself on the fly and this change is kept in memory. POWERFUL processing is needed. Considering the speed and power improvements in Canon DIGIC processors over the years on the camera side, would we not have expected something parallel to this in printers to some degree? There might be surprises under the hood.
Here's another thing to think about in the same vein, compare the specs of the Pro-100 and Pro9000 MKII and MG printers with respect to droplet size, why are the less expensive MG printers sporting smaller droplet sizes, yet the 100 can print with finer grain......the processor and finite control. Same situation for Epson with respect to performance. Finer control of the drop pattern allows it and this is only possible with increased processing power within the print engine. Whether we as humans can discern the improvements is another thing though.