I4 would have been interesting to see, in the very earliest days it seemed like the FIA were going to go with I4, or at least this was the general assumption. I have a few ideas for how the packaging could have been resolved. However I should consider what the combined 1.6L V6 PU output ended up being and whether or not an I4 could supply that and at what fuel flow rate per swept cylinder volume & diameter. At 100 kg/hr, four cylinders at current 267 cc would have been more richly fueled, four at 400cc would have a similar a:f ratio although with a larger CC and associated implications. Was the 267cc cylinder @ 16.7 kg/hr arrangement chosen because of an expectation of its combustion dynamics? If so then the six cylinder count may have stemmed mainly from that rather than the structural qualities of a vee block.
SiLo, was there a production truck with that arrangement? Or rather they had some design studies in their portfolio for such.
Wouter, that article raises a, in hindsight, obvious counterarguement, namely: "blame the losers." Tricky to pull off, maybe, and the last ones to do so were RBers you might say. When Horner "blamed the losers" 2014-2016 for the Renault PU he was criticized as rude.