Traders know very little. They don't have access to that much information right now, and will largely be betting based on what has been a strong launch, albeit with limited stock. The current quarter (April to June) is the major test for the system.
I don't see Switch selling as quickly as Wii did, but I think it could potentially have a long life-span, especially if we see revisions coming along. I'd guess 10-12 million sales in the first fiscal year will be the highest sales range we see. That would be a very good start, it'd put Switch at the 12-14 million mark after 13 months on the market.