Already did!
Gamer seems to be the most liked out of many "banned" stages. If folks could find me convincing arguments to test its legality I bet I could legalize it for maybe one night to see what people thought. At a minimum it might be fun.
I've considered doing an "odd stages" tournament too. Not really stage testing like before, but using the more out there stages just for fun in case any blew our minds. Maybe it belongs there?
I suppose I'm very late to the party, but given that I really like the stage, I'd like to take a crack at this. I've spent a fair amount of time testing this stage out and I feel that Gamer should get more discussion for tournament viability than the zero amount of discussion it's currently getting.
There are two main issues that players have with this stage's viability: 5-Volt and potential caves of life caused by a solid platform that can appear on the stage in the center or on either side of the stage.
The easiest to address is 5-Volt. There are plenty documented ways to avoid 5-Volt's death stare that do not compromise your safety relative to your opponent or your ability to fight, rolling being one of the most effective methods in my opinion. 5-Volt's death stare only covers half of the stage (unless she sweeps the room), so if the fight is taking place on the other half of the stage, she's not even a factor. 5-Volt also serves as a way to prevent campers from sitting under solid blocks, as her knockback can kill a player at kill percentages regardless if they ricochet off the solid ground or not (though I haven't tested teching off a 5-Volt blast yet, I'm certain there's no reason to assume you can't do that.)
Suffice it to say, while 5-Volt can be classified as a monster-type hazard, she's avoidable to the degree of a Halberd hazard; it's very likely your own fault you got hit by her. If Halberd can be considered tournament viable in spite of its hazards, one of which you can be grab-combo'd into, I think we can have a meaningful discussion about Gamer's tournament viability given its own hazard.
And now onto issue number two: The caves of life.
The first thing I'd like to mention after running three sets of 10 matches on this stage is that I'm comfortable concluding that there is a 50% chance you will either end up with a stage form that has a solid platform or not.
For information's sake, here's the breakdown
Set 1: 6-4 Solid Platforms
Set 2: 5-5
Set 3: 5-5
So essentially, it's a straight up gamble that you'd get a stage with solid platforms to begin with.
But that doesn't make up for the fact that 50% of the time that you get a stage that takes away kill options. To address this issue, let's imagine the stage being roughly 5 units long. When a solid platform is in the center, it only takes up the center unit. horizontal kill options are very much viable across the entire stage, with vertical kill options being limited to the left, center left, center right, and right sections of the stage. The top of the solid center platform is also vulnerable to 5-Volt's death stare, which makes camping around the center block a poor strategy. Sure, knocking a player cross-stage will likely result in them ricocheting off the platform, but cross-stage KO's aren't a great kill option to begin with.
Now, the more dodgy aspect of Gamer is a stage form with a solid platform on the edge of the stage. These solid platforms take away two units of the stage, and admittedly this can create a no-kill zone on the Center-Right/Left unit of the stage as well as limiting your kill options on the far-right/left unit of the stage. I don't think I can come up with an objective argument that will perfectly satisfy people on this issue. Personally, I've never had cave of life problems on this stage, having played more than 40 matches in the last couple of days testing Gamer. I know what kill options are viable at each section of the stage and my opponent can't camp in the one area he's safe from kill moves at kill percentage due to 5-Volt and the very limited space the no-kill zone makes up anyways.
Another important thing I would like to point out are the potential caves of life on this stage relative to other stages that are banned due to cave of life effects. As I've pointed out, the cave of life on Gamer, at its largest, takes up less than half of the stage. Compare that to a stage like Luigi's Mansion or Sky World, where solid platforms take up a vast majority of the airspace, which takes away all kill options at every point in the stage. On Gamer, you still have large areas of the stage where all kill options are available to you. The fact that Gamer's cave of life occupies less than 50% of the stage, in my opinion, warrants more discussion and testing of Gamer's viability.
As to what this stage adds to the tournament scene? I still consider myself learning the metagame, but I would guess that players who use lighter characters would be vulnerable to 5-Volt KO grab combos at lower percentages, and characters with deadly juggling and aerial games, like Diddy and RosaLuma would be limited on stage forms with solid platforms. Of course, there's a 50% chance that the stage won't grant these advantages.