Umm...
UMK3, MKT, MKG...?? Its somethng theyve done before and certainly nothing just Capcom does.
They certainly aren't going to repeat the mistakes of the 3D generation, and UMK3 was mainly to correct the mistake of leaving fan favorites out, was it not? Those decisions were made as an arcade company, and the 3D decisions were made as a casual game company.
Point is, they've put deliberate distance between the past and present, and what they want to do with the game as a product.
Theres no reason for them to time travel to a time before DLC. Making an expansion as DLC defeats the purpose of having the ability to sell individual characters and patch the game on its own. To do so now after planning 4 dlc characters and promising more since they sold well, would be shooting themselves in the foot, as they've already sold what would be considered part of the value of a UMK9. IN ADDITION, since they've established these DLC fighters, they would have to draw up even more characters that wont even be in development until after the planned DLC cycle is over, which could be years.
If they wanted to make UMK9, they would never have said "we'll keep making DLC characters as long as they sell well" and they really have no reason not to, unless they were to follow a capcom model and abandon support in favor of a new iteration.