Well, Nissan isn't using it right now.
Ford has been busy filing numerous trademarks for new vehicle names. In the past few weeks alone, the Blue Oval trademarked Splash for a possible pickup truck, Rattler for an off-road trim level, and Warthog for a performance Bronco variant. Most recently, the Ford applied to protect another name that has us asking some pretty big questions. On July 12, 2021, Ford applied with the USPTO for "Skyline." Nissan won't be pleased to hear this news.
The application is pretty vague, "intended to cover the categories of motor land vehicles, namely, SUVs, trucks, and automobiles." Aside from the Nissan connection, we are pretty shocked to see Ford trademark this name because it has never used it on a vehicle before.
Though Ford never used the Skyline name, it did apply a similar "Skyliner" moniker on several vehicles in the 1950s. The Skyliner name appeared on the Crestline, Fairlane Crown Victoria, Fairlane 500, Galaxie, and most recently on a Ford Transit Concept vehicle in 2014. Dubbed the Ford Transit Skyliner, the concept was built by Galpin Auto Sports as an ultra-luxurious van. Ford called the Skyliner concept a "private jet on wheels." Though they have a historical context, none of these options seem likely.
Of course, most car enthusiasts know the Skyline as the Nissan model that underpinned the performance GT-R variant until 2002. Nissan still builds the Skyline as a four-door sedan, essentially a rebadged Infiniti Q50, though it may be discontinued soon as the company shifts towards SUVs.
This trademark comes so far out of leftfield; we aren't sure what Ford intends to do with the Skyline name. It could make sense for a future Lincoln model now that the luxury brand has ditched its alphabetic naming scheme, or it may go unused like most trademark applications. If we had to take a random guess, we think Ford will add more roof options to the Bronco, and Skyline sounds like a great name for one, possibly a power-retractable unit to rival Jeep's One-Touch Sky Power Roof.