If he is so popular and isn't expendable why is he left out of some of the versus games?
Marvel vs. Capcom - Capcom included 4 fighting game ports and 4 brand new characters, each assigned to a different fighting archetype: Ryu and Captain Commando are the standard characters, Morrigan and Mega Man are the technical characters, Chun-Li and Strider Hiryu are the speed characters, and Zangief and Jin are the power characters. Ryu can transform into Ken, but there wasn't any room for him on the actual roster.
Tatsunoko vs. Capcom - Producer Ryota Niitsuma wanted to include only one character per series. Ryu is from SF1, Chun-Li is from SFII, and Alex is from SFIII.
Marvel vs. Capcom 3 - Niitsuma didn't want to include characters who are too similar to one another. Ken would have been considered too similar to Ryu.
Again, the Vs. games are not a litmus test for anything. Zero made the TvC and MvC3 rosters over X, but that doesn't mean X is expendable from the Mega Man X series.
Also I'm not saying they are definitely going to leave him out or even that he won't be in at all, I'm merely stating it's a possibility he might not be in the starting roster.
Anything is possible, but you shouldn't throw the word "expendable" around. There are something like 20+ games with "Street Fighter" in the title, and Ken is playable in every single one of them. That's the exact opposite of expendable. It's not Street Fighter without Ken.