Capcom has announced that they are not planning on adding any new Street Fighter characters as DLC. Here’s the reason they gave for that decision:
“No plans for additional DLC right now. We want the core game to be a completely functional package, and character DLC could split the user-base.”
They also stated that there will be other DLC packs coming that don’t affect gameplay, such as what was included in the Championship Mode DLC. But of course, they could simply give the DLC away for free. That way everyone would have the extra content.
[Source]
