What you're talking about with the mods is essentially just having another hotbar activate when you press a button. You could make a keybind to swap hotbars in game now and get the same effect. Also, if they actually implement something properly, they'd need to get graphics designers involved, make sure it plays nicely with all the other UI elements, and do extensive testing and iterative design on it. Making UI elements is easy. Making good UI elements is more involved.
Also, as I said earlier, the button bloat issue is also related to the fact that classes only get class actions at level intervals and the number they get in one interval is very small.
As for the gauges, I may have misinterpreted the OP, but this new summoner already has a bar for each element.
Again, people will just choose whatever summon that gives the best DPS. Things like paralysis or DoTs vs direct damage are mostly inconsequential in raids. Even if they do have compelling options, they'll decide which element to build up right at the start since the system doesn't favor switching easily. After that, the rotation you suggest is very set since there will be a cycle that is best at building the appropriate element, meaning you'll just cycle mindlessly through your buttons until you can summon something. There's only one instant of decision making in the whole rotation.
You'd need to add other mechanics to make it necessary to deviate from the standard rotation. Samurai does this by having both sen building and big buffs tied to their three combos, so you need to balance sen generation, buff uptime and buff priority. This means that, especially when buffs fall off due to mechanics and the need to have exactly 1 sen with at least your damage buff up every minute to re-apply your DoT, you need to constantly be thinking about your next combo.
You need to add some sort of dynamic element that will promote these second-to-second combat decisions without removing control over which element the player builds.