What about a break away sect much like the ones that led the Taiping rebellion,with YHWH worshipped along with other gods,and have the Christian features of charity?
Taping rebellion was fueled trough an anti-Manchu take : Roman society was too cosmopolitain to really build something like this on it.
Not that
popular revolts didn't existed, but they were more fiscal than anything else and eventually crushed, and given social religious practices, wouldn't really have room for a religious part critically when, at the difference of Europeans and Christianism in late Qing China, such syncretic pantheon would hardly look as an ever-victorious entity.
If an emperor gave it personal patronage,would it have been popularised?
Strictly speaking? Not much. Even when Christianism recieved imperial patronage, it took centuries (and more religious driven Romano-Barbarians rulers) to have a Christian majority westwards.
As for coherency,wouldn't the religion 'evolve' over time to become coherent?I mean we had a crap load of gospel telling different things before the Church decides to limit it to a small number.
It could, but would barely have room to do so : Christianism would still continue to evolve independently, and would have more success than a patchwork-esque pantheon (assuming that imperial successors doesn't decide to switch back to less incoherent rites, as Mithra or Sol Invictus and that would be immediatly more useful politically).