Overwatch has been one of the most highly requested games for the Nintendo Switch, but Blizzard has been holding out on the fans so far. It seems that the fans are doing Blizzard's work on their own, as it's possible to run Overwatch on Nintendo Switch by modding the system.
Blizzard has previously discussed the idea of porting Overwatch to the Nintendo Switch but has downplayed the chances of it happening. The reason for this is due to how difficult it already is for the company to regularly update the game across multiple systems. The Nintendo Switch has since taken off in terms of popularity, but there is also a lot more competition on the system in the form of Fortnite, Paladins, and Warframe, as well as an abundance of first-party titles coming in the next year, so Overwatch for the Nintendo Switch must seem like an unappealing prospect.
It seems that it's easier to port Overwatch to the Nintendo Switch than anyone realized. The switchroot modding group has uploaded a video to Twitter that shows Overwatch running on the Nintendo Switch. The Nintendo Switch has been modded to run a version of Android and NVIDIA GameStream, which can run a version of Overwatch remotely from a PC.
All of this is accomplished with the aid of unofficial mods and it's likely that Nintendo will attempt to go after the people responsible for jailbreaking the Nintendo Switch in order to run Android, as they have done with so many other modding groups in the past. There have been many attempts to hack the Nintendo Switch based on its Tegra X1 chip, which is notorious for a series of technical flaws that have allowed hackers to perform all kinds of mods with the system.
There are rumors suggesting that Blizzard is currently working on a sequel to Overwatch, which means that it's possible that the company will wait and release that for the Nintendo Switch instead. The fans who are willing to mess with their Nintendo Switch can get Overwatch running themselves, but it will take a lot of work and there is a real risk of bricking the system.