Speculations about the possibility of a new Mortal Kombat game being announced or shown at E3 2018 have been going on since the start of 2018. It seems there may be some truth to it, as Ed Boon has posted several Mortal Kombat teasers.
Mortal Kombat fans have flocked to Ed Boon's Twitter after he conspicuously noted that "Klout" were doing their spelling right, hinting at the way Mortal Kombat series used letter "K" instead of "C" in almost any situation.
Now, some fans didn't take the hint the first time around which resulted in one of them saying that Injustice 2 getting Fighter Pack 4 in 2018 "would be cool". This prompted Boon to tease the new Mortal Kombat once again, by saying "You know what ELSE would be kool...?". With that second "K" hint, Boon all but announced the next Mortal Kombat game.
Normally a random tweet that references a product of a specific company wouldn't be much to go one but NetherRealm Studios developed a pattern with teasing new games, announcing them, releasing DLC and then starting all over again. The two series in rotation are Mortal Kombat and Injustice.
Mortal Kombat Komplete Edition marked the end of production of DLC for the game and it was released on 28 February 2012. Injustice: Gods Among Us was announced three months later, on 31 May 2012. The game had its Ultimate Edition released on 07 October 2013, which was followed by Mortal Kombat X announcement on 02 June 2014, which landed just before E3 that year.
The definitive edition of Mortal Kombat X came on 01 March 2016, and Injustice 2 was revealed on 08 June 2016. You guessed it, the reveal happened just before E3 again. Legendary Edition of Injustice 2 came on 27 March 2018 and E3 2018 is just around the corner. You know what time it is ladies and gentlemen - it's Mortal Kombat 11 announcement time.
That said, we shouldn't get ahead of ourselves as a 2018 release will be highly unlikely, with Q1 2019 sounding a lot more reasonable.