Things to take into consideration:
Since we're talking about mechanical keyboards I'll assume it's for the gaming brand products. A large portion of the mech keyboard community are typists so I'd take anything mentioned with a grain of salt.
Forexample: I'd never bother with kailh brows, or beamspring or 65+g switches for games. Finger fatigue. Good for typing but not games.
I overly prefer switches with high actuation points and low total movement distance, even going as far as using o-rings just to reduce max move length before bottoming out on keypresses. Things like that are loathed upon by some people.
Also I think it's already been understood by logitech people at this point, don't make overly gaudy chassis designs. It's dumb and people don't like it. Don't use nonstandard layouts or keycaps, people like to be able to change keycaps.
Also gaming stuff:
Mount the space bar in reverse. Space tends to be used a lot in any genre besides RTS. With reversed spacebar the thumb rests against the flat sloped side of the bar rather than against the edge.
Make SPILL PROOF designs. That includes having gap in the frame to allow excess liquids to spill out on the side alternatively use frameless elevated keys designs.
Make the keyboard heavy, include a plate. This has nothing to do with the quality but self proclaimed "keyboard" experts will insist that the keyboard feels more "solid" as a positive feature.
RGB rakes in the money but please make the backlight either white or blue on non RGB but backlit products as one is neutral and the other fits with lots of other desktop stuff that typically has a blue light as power indicator.
Have dedicated light for caps/num/scroll lock, don't make use of leds below the actual keys. That feels cheap.
"gamers" love dedicated media buttons for unknown reasons, don't make those as hotkeys from key-combos, add them as extra buttons on top or something.
Measurable parts of "keyboard quality" brings up 2 things: Consistency and speed.
Consistency means how consistent keys are. All keys should preferably feel the same ie. actuate at the same height and require the same pressure to actuate.
Speed means how fast it takes for the signal to register. People generally never pay attention to this, and higher actuation point saves more time than the few milliseconds from optimized architecture. The other thing is debounce. You want as short debounce as possible, which is of course limited mechanical debounce that comes with the switch design, unless if something like optics or magnets are used.
:e oh no its a necro thread barrf