Looking at past threads like this one for the wii u;
http://gamrconnect.vgchartz.com/thread.php?id=147642&page=1
Turkish was the easy winner with less than 20 million and still someway off the final figures which surely can't exceed 15 million. So was actually pretty optimistic compared to the final figures. The average prediction figure seems to have been around 40 million with some figures as high as 150 million.
Of course making accurate predictions is near enough impossible because we don't know what decisions Nintendo will make. Price drops, new sku's etc.
Some of the problems the Switch has;
1. Very low performance level for price as a home console (cannot be solved)
2. Very limited range of software (high unlikely to ever be competitive)
3. Very low performance level of software for home use (cannot be solved)
4. Very high pricing of accessories (can be solved)
5. Very high pricing of retail games (can be solved)
6. Short battery life in portable mode (can be solved with later sku)
7. Online subscription cost with few online games (can be solved)
8. No subscription loyalty bonuses of full games compared to competitors (can be solved)
9. High pricing of download games (can be solved)
10. High cost of publishing retail games due to cartridge costs for third parties (realistically can't be solved)
11. Poor controllers for conventional games (solved by additional purchase)
12. Once included controllers are discharged cannot continue gaming until charged (docked) (can be solved by additional purchase)
13. Poor range of upcoming titles (unlikely to be solved)
14. Limited storage (can be solved at additional purchase)
15. Maximum 1080p resolution for home use (cant be solved with this sku)
16. May have limited retail support (can be solved)
The positive
1. Good portable performance
2. Mario IP
3. Zelda IP
4. Nintendo's own software range
5. Merging of portable and home software developers to support one format
6. New controller functionality to add to gameplay experience
7. Possible low cost VR accessory being launched which takes advantage of tablet format of console
