AirPlay Mirroring and iMessage are arguably two of iOS' biggest features without an OS X equivalent. According to 9to5Mac's ever-popular "sources familiar with the future of Mac OS X," both components might find their way into a future version of Lion. In the publications' own words, "Although neither project may see the light of day, they are definitely on the table for release."
Universal iMessaging across all Apple platforms seems only natural — especially given its ubiquity across even non-cellular iOS devices like iPads and iPod touches. As for AirPlay mirroring, the most exciting use case we see is watching Hulu on the big screen without paying for a Plus subscription and without having to tether your laptop via DisplayPort wires. Both of these features would definitely be considered high profile, so don't go expecting any of these to come out on a random weekday as mere bullet points without much fanfare.