Ed Boon and other members of NRS said that they wanted to support this game with DLC for a long time. Therefore I think they will release costumes, characters, fatalities (including stage-fatalities) and entry and victory poses.
NRS has already released a classical costume pack and labeled it as the first one, implying that more will come later one, because the first one just gave you the unlock keys for the costumes/fatalities. Also the game itself already contains more classical costumes in form of unlock-able fights and they released in the compatibility packs also classical costumes. I presume that in one year every fighter will have their MK1, MK2 and MK3 or another classical costume if they didn't had already MK1. MK2, MK3 costumes. But let's see the possible costumes for each character:
Bold means that this costume is already available and selectable
Italic means that this costume is available but not selectable (Hidden Noob and Smoke)
Sea-green means that further details will come
, MK2, UMK3
Jade: MK2, UMK3
Jax: MK2, MK3
Johnny Cage: MK1, MK2, UMK3
Kano: MK1, MK3
Kenshi: MKDA, MKA
Kitana: MK2, UMK3
Kung Lao: MK2, MK3
Liu Kang: MK1, MK2
Mileena: MK2, UMK3
Quan Chi: MK4
Raiden: MK1, MK2
Rain: MK1, MK2, UMK3
, MK2, UMK3
, MK2, UMK3
Shang Tsung: MK1, MK2, MK3
Skarlet: MK2, MK3
Sonya: MK1, MK3
, MK2, MK3, UMK3
Cyber Sub-Zero: -
Kenshi: His real alternate could be his Deadly Alliance alternate costume and as a classic costume he could receive his Deception/Armageddon costume with the ? character (meaning: sky, celestial, godly)
Liu Kang: There is only one small difference between his MK2 and MK3 costume, his hair. They could release it because it isn't much work.
Rain: Ninja costumes are simple palette swaps and even Smoke and Noob got MK1 costumes, therefore a chance by seeing Rain in a MK1 and MK2 costume are there.
Sheeva: The chances for this costume are very slim because there aren't any noticeable changes between her MK3 and first MK9 costume.
Skarlet: Skarlet was a glitch in MK2 therefore a MK2 costume is plausible and a UMK3 costume would be just a palette swap with her sheathed weapons therefore possible.
Besides the classical costume flood at least one new alternate will be definitely released, because NRS had many ideas and concepts just look into the art-book. Costumes are a definite DLC.
NRS made in early interviews clear that fatalities are something they wanted to include, moreover they bragged about the bell tower fatality and it hasn't been released yet. Fatality packs, which probably will contain up to two new fatalities for each fighter making 4 fatalities (without the stage fatality). Fatalities are not per-rendered animations they are just a simple instruction file, that tells the engine what to do. Just look up the size of CHARACTERSNAME_FATALITYX.XXX files. Also they will include stage fatalities at one point.
After the release of the ??? character. NRS will release the last MKT characters meaning Chamelon, Khamelon, Motaro as a sub-boss and Cyber-Smoke (if he wasn't the ??? character). After this only this characters might have chance.
Hornbuckle, because just like Skarlet he was/is just a rumor and the rumor Skarlet has also been turned into a character.
Daegon, Reiko, Frost, and Sareena because they are shown as Pit fighters and Kenshi, who was also a Pit fighter has been already released. But if they are going to release them all they have to create another Pit fighter to close a logical gap which will come out if four of the former Pit fighters have been chosen in a tag duel. There are only five pit fighters but they would need six fighters in order to let two Pit fighters fight in the background where the other four are fighting in the tag duel.
Tanya, Kitana, Li Mei and Kira because they are slaves in Shao Khans Colosseum. In this case no logical gap will arise because the places can also be empty.
And Fujin because he has been indirectly announced.
I believe they are going to release one new X-ray per character. It will be a counter move if the character hasn't got one or a normal executable X-ray if the respective character had a counter move before. Making two X-Rays per character. A dream would be the following scenario:
One counter X-Ray
One close combat X-Ray
One long ranged projectile X-Ray
It could be realized but we will see it after the first X-Rays are out.
5. Victory and Entry poses
This is the thing for which I wish more than costumes and characters at the moment. There is another set of victory poses already in the game. Just you look at the challenge tower missions. They will include these poses into other modes first and give the characters one new victory pose. As well as one new entry pose. But in the end I wish that every character would have four entry poses and four victory poses. This would really help to reduce repetitiveness.
Brutalities: They could come out but then they should give each character a specific brutality and not making one global brutality like in UMK3. Also after seeing all the fatalities I have really high hopes for really good brutalities without meaningless explosions and infinite bones and skulls. I presume they will heavily rely on the X-Ray feature for them
Friendships: They could come, by animating them right they could be even good and funny.
Stages: The will definitely not come at least not from NRS sides, there could be a chance of bringing NRS to the state of releasing them with a huge petition, which shows the amount of interested people. The amount should be around 500 people. Nut please consider a price span from 5$ to 15$ per stage. The stages that would make sense in this game are:
The Pit (Because the Pit in MK9 is the MK2 Pit not the MK1 one, but they could include the MK2 fatality for it)
Noob Saibot's Dorfen
Pit 3 (Could be under Khans Throne room if they want to implement it according to the new storyline)
Other MK Games
Wu Shi Academy makes sense because it's in the story mode.
Well that are just my thoughts I ordered the to be released contents by their releasing probability from the highest to lowest probability.