The fighting game genre is a solidly defined genre, it doesn't need to be "modernized". It already has like 3 subgenres going on, traditional fighters (2D: Street Fighter, Mortal Kombat, BlazBlue / 3D: Tekken, Soul Calibur); non-traditional fighters (Dragon Ball games, Smash Bros.) and the sports simulation games (UFC, WWE, etc). Then there's the divide between casuals (they aren't that competitive, care more about just messing around with friends and single-player) and the competitive players (they play online a lot, go to tournaments, spend time in training mode learning things about their character).
Thing is, the most popular of these is the traiditional fighters and the people that really like that genre mostly care about getting a mechanically sound and properly balanced game more than anything. There's not really much that can be done to modernize the genre and I feel that it has already been evolving well enough, with 3D graphics and new mechanics.
The traditional fighters mostly differentiate themselves through their unique style, characters, control schemes, mechanics and movesets. Look at Marvel vs. Capcom 3, it diferentiates itself from Street Fighter by being a much faster paced combo-heavy game, 3v3 fights and featuring more "out there" movesets than Street Fighter. BlazBlue differentiates itself with the "Drive" system that basically gives every character a unique gimmick. Persona 4 Arena differentiates itself with the titular Personas assisting the characters. Tekken differentiated itself by being one of the first 3D fighters and it still is the most popular one.
So the genre already has a lot of variety going on and I can also assure you that the new fighting games feel very different from old school ones.. For example, the games now try to feature more new mechanics to make them unique. Back then, we had like Mortal Kombat trying to differentiate itself from Street Fighter by simply having realistic graphics and gore. Now we have more unique mechanics in each game, like I mentioned on the previous paragraph.
They also try to bring new players in more, try to ease them in so that they might try to be at least semi-competitive. Back then, tutorials were rare if not inexistent and a bunch of games didn't even include a training mode in which to mess around without having to mess with the AI.
It is also one of the genres that favors online gameplay most, due to it being a very competitive genre, you could spar with real people at any time (though sometimes it seems that the developers don't put in enough effort into their netcode, sadly).
I didn't mean this post to be so long, but... yeah...
