Mm... yes and no. The issue is that given how the hotbars work, it would likely have to be a second copy of the entire combo... or you would need a sort of hotbar action abstraction system (which I suspect is how the mod that consolidates combos in PvE likely works).
The latter would be the better approach, honestly. Especially because you could then functionally make it a 'build your own combo' system; instead of "here is a pre-made button that is your entire chain", you would just have a little hotbar-like list you could drag actions onto, then you'd drag the icon for that list onto a hotbar. Each time you pressed the button, it would send the current action, and advance one step.
For those who just want their 1-2-3 on a single button, that handles it easily. From an accessibility standpoint, it wins for flexibility because someone could put a mix of GCD and oGCD into a single button. For instance, someone could make a combo button that was (to use SGE as an example) "Eukrasia" followed by "Prognosis", and then they could just hit that button twice quickly to do Eukrasian Prognosis.
I've mentioned this in other threads touching on accessibility, but back in the WildStar closed beta I had a dear friend who had severe nerve damage to his hands from his time in the military. He could barely type coherently when his hands seized up, and hitting any sort of precision button combo was... let's just go with "a non-starter" at those times. The solution I came up with for him was something sort of like what I describe above: I wrote a tool that let him create those sort of combos, and then bind it to like... 6-9 different keys. So, for instance, he might have an attack rotation in a combo cycle that was bound to `, 1, 2, 3, and q. Then as long as he hit that general area of the keyboard -- which was doable even when his hands were seizing up -- he'd do the action he meant to. And there was a keybinding to toggle that mode on and off, so he could also (try) to type normal text in the chatbox.
Unfortunately, he passed away due to pneumonia before I finished the project, and I lost heart and handed the code off to someone else. (Get your flu shots!)
But if we want to approach the PvP-style combos in PvE as an accessibility thing, I think I'd rather do it more like that -- a more open-ended system, that can address more use cases -- than simply consolidating the 'stock combos' each into a single cycling key. Especially since that solution would allow people both to do the consolidated combos or to leave the actions split across multiple separate keys, as best suited their taste.
(Sorry, accessibility is a thing I have come to take very, very seriously in game design.)