If they don't ship before the holiday season, they'll be setting themselves up for failure. Apple will be releasing a new iPad in February, so the consumer market will be toast for them. Tablet growth continues to explode, and by the end of 2013, it's conceivable that tablet sales will outpace traditional PCs:

http://www.asymco.com/2012/03/02/when-will-the-tablet-market...

In a BYOD world, can enterprise sales provide enough traction for Microsoft to overcome their lack of appeal in the consumer market?

EDIT-

It appears the low end model will be out in October in time for the holiday season, and the Pro version 90 days later.