Given the uproar over gems in SFx Tekken, I’d have to say the reaction would be pretty bad. The ideal solution would be to provide things like cosmetics and costumes rather than characters, because anything that effects character balance is a no-go zone. DLC characters are usually considered an after thought or a promotion if anything, and players tend to regret having to spend money on characters they feel they should have had to begin with. Hell, fighting game players hate to even spend time unlocking characters these days 
In any competitive game with a competitive community though, the highest tier players will have an ego, and just like an MMORPG you can capitalise on that ego by offering ways for them to customise their character and otherwise ‘stand out’.
Custom hitsparks, hats, costumes, tattoos, voices, taunts etc. People would buy these things. If you say, released a street fighter game with the option to buy MVC2 hitsparks for your character and stick Ryu in a Megaman helmet while giving him Bad Cover Art face, someone somewhere is going to jump for their credit card.
The best thing about this kind of microtransaction is that you can give players a large variety by designing a lot of small content and selling each for a relatively cheap price. It’s much easier to convince buyers to spend money if the product is cheap and plentiful as opposed to expensive and singular.
Cash Shop MMO’s can get away with selling items that effect game balance because of the nature of such games, but this is generally considered ‘pay to win’, which is a very negative stigma to have attatched to your game. MMO’s are usually a lot more casual too, and their communities much more forgiving.
But yeah, if you can unlock everything by playing legit for a certain amount of time, and just have the OPTION to buy all characters outright to avoid having to unlock them, that might satisfy some players, but then at the same time a lot of players would be saying “I’d rather buy the game full price and avoid having to unlock anything!”