IMO, one of the biggest concerns, aside from some truly stunning conspiracy theories, is a sizable enough portion of the backers selling their figures on the secondary market to the point that it impacts retail sales noticeably, doubly so if it's backed with an ongoing sentiment that the figures are a pain to build in the numbers needed for large scale games.
Large scale games being desirable as it means people end up paying thousands of dollars over the years to build up 5 squads of ______ and 10 squads of _____ and 14 _______'s, etc. If the community/playerbase says "Eff that noise" and is content to buy a core box and a couple of expansions, it's not exactly going to fly off the shelves.
It comes down to supply and demand. If the demand is low and the supply is high, the price drops. Who is going to pay $30 (20% off MSRP) for a VT box if they can get them on ebay or craigslist or kijiji for $25 or $20 or less? And while that may eventually balance out (depending on how many players and collectors are actually out there and willing to pay for boxes), as the number of dissatisfied backers is surely less than the total global demand, in the short term it could do enough harm to distributors and retailers (sites and physical stores alike) to cause them to drop or rein in their stock needs.
With 2 shipping waves and who knows what else, presumably the goal of PB, ND, HG and their associated distributors and retailers is to make money, and soon. If there are weeks or even months of people pitching their boxes onto ebay to overcome, that's basically a double loss; one person who was a 'sure thing' is now getting out, and someone else who *would* have bought models from stores is instead taking them off Player One's hands.
Not to mention the damage that negative buzz and word of mouth can have. Even a sterling reputation can tarnish, and I think we can agree that there are certainly some sentiments out there in the wider gamer community (some deserved, some not, but present all the same) that are less than positive.
Of note, this isn't meant to be all "DOOM AND GLOOM! FOR WOE THE END IS NIGH!", I'm merely pointing out that there are business considerations to this. Early on, when some consumers and retailers may be skittish of 'yet another game', where nostalgia might overcome reluctance, is a vulnerable time. Even with the KS backer funding, that money only goes so far, and they're presumably going to want to turn this into a positive revenue stream sooner rather than later.
And depending on how this works out, that could be a problem.
But I'm sure they'll keep their word, fire off 'mouth watering minis' to the backers in June and have piles of boxes to rake in some sweet, sweet Gencon money with.