Busan, as you may be well aware is a city in Korea and when Blizzard decided to add the map set in the city to Overwatch, they didn't pass up the opportunity to add some of the local flavour, such as the love for dance games and karaoke.
We were aware that there was an arcade with a DDR dance pad for a few days now, thanks to the video from PTR embedded above, but it appears that it's not the only Easter egg in the map.
First things first though, the machine shown in the video can entice players to emulate dancing on a dance pad by following the directional controls, but their character will not perform a dance emote unless players make them manually do so. You can see Torbjorn and D.Va showing their dancing chops above.
One would expect that D.Va would also take the stage and be the main star when karaoke is in question, but as it stands now, it appears Reinhardt stole the show. Overwatch's grandpa in power armour will be able to go to the karaoke room in Busan where he will be able to interact (F) with the microphone, which will cause him to go freestyle by uttering "Sexy, sexy Reinhardt!".
Apparently, he is the only one who can interact with the microphone on PTR at the moment, but it's not excluded that more heroes could get lines once the map hits live servers. It could definitely become a thing due to this particular Easter egg's popularity, which has even sparked a fan made remix that includes Reinhardt's line above.
The singing talents actually managed to help the old man get some press coverage, as the hamster in power suit has been hogging all the attention lately.
That said, it would be great to hear Winston and Hammond perform their own lines at the microphone, but Roadhog definitely has the ultimate potential for hilarious lines.
Busan arrived to PTR only recently and there is currently no official release date.