At time of publication, both accessories show shipping estimates of 4 to 5 weeks. According to Mashable, an Apple spokesperson has responded to the matter and assured customers who have pre-ordered the accessories that they will receive them.
Mashable - “Customers are very excited for iPad Pro, Apple Pencil and the Smart Keyboard," an Apple spokesperson told Mashable. "We have limited supply of Apple Pencil and the Smart Keyboard in Apple Retail stores. Our stores will continue to receive regular shipments and we encourage customers to visit Apple.com for online availability and delivery dates.”