It is extremely tricky to not be gamed and sybil attacked. The best we have come up with thus far is PoW and that is far from perfect. It would be great to roll out some tests on a sidechain and attempt to game them.
i agree that knowing what versions people have can then be sybil attacked by biased people adding a crap tonne of nodes of their particular preference.. but the flip side is that the different band camps can argue forever saying team gavincoin is winning.. then 2 seconds later team blockstream say they are winning without either ever having to show proof.. because they both wont allow or trust actual version statistics to be publicized, and if then publicized they'd simply debate more that the numbers must be fake.
id say its not impossible to get a fair understanding of what the implementation preference is, just not easy to guage what is honest numbers versus sybil attack numbers... impossible is too strong a word..