My understanding is that there should be another pre-sale next month, and the month after, etc., for another 500 scopes. I may be imagining that or it may be what I suggested they should do...
As for why put a cap on pre-orders, even with a $100 down, there are going to be some people who decide they just cannot afford another $899 charge when the time comes to pay for the complete scope. Additionally, we have already seen how easy it is to overwhelm Unknown shipping departments (e.g., I'm still waiting on a Black Friday suppressor to ship). Spreading them out at 500 per month may well make it easier to predict flow rate and hire the right number of people for the job. Anything with a six-month lead time is going to require some artificial way to regulate supply until they get to the point where they can afford to keep sufficient inventory in stock to handle "normal" demand.