yeah, there are a lot of reasons to not allow that. For instance, Friend 1 comes over and falls in love with the concept of a GF and wants you to add one to your order to allow them to get their machine sooner.
But on the flip side, say you wanted one because of your business. Well, now with the delay from June, you have grown your business and now a second one is not only feasible but now it could really help further boost your business. It would be awesome to add another to your spot in line.
It all depends on the purpose and risk associated and who is assuming most/all of that risk