It will probably happen eventually for linear combo paths. It was decent when there were fewer abilities and difficulty had to come from somewhere, but most difficulty now comes from buff/dot uptime management, proper oGCD weaving, and mechanics of the encounter itself.

It'll still get the usual cries of 'oh no this will ruin the game', 'I'm unsubbing', and 'we're becoming the game which most not be named', but in truth most classes would barely feel the change because almost every combo in the game branches. PLD for example: Savage Blade and RoH become a single button. That's pretty much it. Fast Blade combos into 2 different abilities so you can't make that a single button. Same with Riot Blade. It's basically just a QoL change to reduce hotbar clutter, but people will still dig their nails into their armchairs about how gamebreakingly bad it's going to be because the benefit of the change isn't immediately obvious.