This is an interesting hypothetical, but all but impossible given the degree that Sony disrupted--nay, obliterated--the videogame industry.
First of all, without Sony, both Sega and Nintendo would have released less powerful consoles. We all know the stories about the original Saturn design, and how Sega was forced to increase the hardware power to compete against PlayStation, at the cost of having a console that was brutally expensive (which is ultimately what killed them). We don't know as many details about Nintendo's original design plans before 1993, but we can clearly see their struggles to release Nintendo 64 while also hitting that crucial mass-market $149 price point. They had to literally strip that motherboard down to the bone, like Matt Damon's rocketship in The Martian. That's why N64 was plagued with those infamous bottlenecks & everything was chugging along at 10 fps.
So without Sony, what would Generation 5 look like? I think it would probably look a lot like the Atari Jaguar. That console was designed along the longstanding technology curve tempered by price. You have to build the most powerful console that can also be sold at $149 without losing money. 3DO was a very powerful beast but launched at $700, and even by 1995, it was selling at $299. Needless to say, it never went anywhere. Atari Corp had a much better balance between price & performance, and if they had a better launch--if they weren't crippled by supply & distribution problems in Christmas 1993, if there was better launch software--things might have turned out very differently. Sega was right to worry about them. The Atari 7800, after all, had outsold the Master System in the US ( a little apples-to-oranges, but still), and the Lynx was an amazingly powerful handheld that was crippled by poor distribution (the Tramiels' notorious business antics had caught up with them).
By 1994, Jaguar had some great videogames: Tempest 2000, Alien Vs Predator, Iron Soldier, Doom, Wolfenstein 3D to a lesser extent. However, by that time, everyone was already buzzing about Sony's PlayStation, and so Atari's crucial moment had probably past (those titles should have arrived the year before). And once gamers got a look at Ridge Racer and Toshinden (ugh), that competition was over. Take all that away, and the future looks very, very different. Games like Iron Soldier, I-War and Battlesphere (released after the Jaguar's retirement) suddenly look a LOT better. It's too bad that Space War 2000 was never completed, I really enjoyed that one very much.
So, in terms of 3D polygon powers, we would expect 5th Gen games along those lines. You'll have one more console generation that refines and perfects 2D videogames with some continued forays into 3D, but nothing that represents a definitive paradigm shift until you get to the 6th Gen. You're certainly not going to see something like Tekken 3 or Fighters Megamix during that era.
Now how would the market react to that timeline? This issue is rarely discussed, and was raised here on NeoGAF, but the US videogame industry went into a steep decline in the mid-90s. From 1993-1996, the industry shrank from $6.5 billion to $2 billion. It only really started to pull out with the launch of Nintendo 64 and the subsequent Sony-Nintendo war in 1997. Without Sony in the picture, does that even turn around? Or does Nintendo completely dominate once again? I suppose it would all depend on what Super Mario 64 looked like, and that would depend on what Nintendo's console would be. Would the CPU be 32-bit or 64-bit? How many other N64 features would be gone? Could such a console run Mario? Are we looking at polygon graphics like the Jaguar, or perhaps those early third-party Saturn games that used only one CPU?
One thing is for certain: the kids were growing tired of the same old videogames. The enormous blockbuster success of Street Fighter 2, Mortal Kombat and NBA Jam masked a very sharp decline in the overall industry, and given how notoriously fickle the gaming public was at the time (just ask Sega), something new was needed. Yet another console cycle of refined 1980s-style 2D games just wasn't going to cut it. The kids were not going to tolerate another five years of Donkey Kong Country clones. Without Sony, where does that new innovation come from? Does it come from PC? Doom was a massive megahit, and Windows 95 showed Microsoft was taking videogames seriously. But they only did so because of Sony, and feared losing the living room which was to be the home of the legendary "set top box," where all the futuristic technology predicted decades earlier would converge. Without PlayStation, does Microsoft stick to the PC, expecting that to become the center of the digital future?
The truth is that's the real reason Sony got into the videogame business. They wanted a foothold in the living room so that they could control that future market, one where you could watch movies, surf the internet, conduct online shopping, download music, yada yada. Sony built the PlayStation so that they could sell DVDs and Blu-Rays. Take away the PlayStation and all of that either moves back several crucial years, or disappears entirely. Who knows? Maybe we'd be watching movies on Super VHS?
Counterfactuals, alternate timelines, it's all but impossible to speculate. Sony's PlayStation was a massively disruptive product that changed videogames and consumer electronics in every conceivable way. It was the asteroid that wiped out the dinosaurs and cleared the path for the new century. And there really wasn't anyone else with the vision to make that happen, not Phillips, not Microsoft, certainly not 3DO. Atari Corp was slowly fading into extinction, Sega was that cult favorite local band that had a couple breakout hits, and Nintendo, well, they'll always be Nintendo. They're never going anywhere. How videogames in the 90s would have looked is anyone's guess, but it almost certainly would have been smaller, weaker and less interesting.