Microsoft is making some sort of major announcement next Monday, June 18, 2012, and multiple sources indicate that the company will be revealing its first tablet device. Some say that the intent is to directly compete with Apple's iPad while others suggest something more in line with the more budget-friendly Kindle Fire. It's all speculation for now.
The report first popped up at The Wrap, noting that Monday's "secretive event" scheduled for 3:30pm PST would include some sort of undisclosed "major" announcement. The site was then told by "an individual with knowledge of the company" that Microsoft would be revealing an in-house manufactured tablet. AllThingsD later corroborated the report, noting that its own sources had been saying pretty much the same thing "in recent weeks."
I think that between the SmartGlass reveal at E3 2012 and the shifting focus in the market toward more portable computing technology, not to mention the cross-platform focus in Windows 8, it's only a matter of time before Microsoft introduces its own tablet to the market. Next Monday seems like a great time to do so, so sure, why not?