The theology of Sino-Christianity (as Taipingism may come to be generally known outside China, altho Chinese may just call it "Christianity") wasn't any farther from traditional Christian theology than Mormonism, and arguably was closer.
Agreed.
However, there is one respect in which the Taipings' actions were both well-documented and reprehensible, and that is their treatment of Manchu noncombatants. In OTL, when Nanjing fell to the Taiping, not only did they massacre the Manchu soldiers at the garrison there, but their families as well. In this ATL, the fall of Beijing and extention of Taiping rule over all of China including Manchuria, would have resulted in an even larger slaughter, quite possibly even an extermination campaign against all of China's 5 million Manchus, whom Hong Xiuquan believed to be literal devils.
If so, the historical record of the Manchu genocide could create long-term problems for acceptance of Sino-Christiany outside China (where of course it would be whitewashed from the history books). Opponents of the religion could convincingly argue: How could anyone who presided over the murders of so many women and children, be the brother of Christ? .
There are Old Testament precedents. Unless Taiping Xtianity causes Christianity itself to evolve differently, however, I expect that this would become a problem.
To a certain extent because of interdenominational polemics though these might be muted both because most Christian denominations have regrettable incidents in their own past, or feel guilty about their support for colonialism, or whatever, and because Western guilt (and condescension) is likely to give them a pass. ("We shouldn't criticize the Chinese Christians, it shows a lack of understanding of their past and unique cultural conditions, and, also, you can't expect them to really get what Christianity is about anyway.")
But I expect the main source of Christian criticism to be internal. I do NOT expect that Taiping Christianity will successfully remain a monolothic arm to a continuous, oppressive, authoritarian state. Which means that at some point Taiping believers are going to have to accommodate their past. They're going to have to accept that the Manchus were literally devils (a position that will be hard to sustain in today's world) or else come up with a theology that is much more accepting of destruction and violence than mainstream christianity today or minimize Hong's role in their religion.
However, I do expect significant criticism from non-Christian westerners. The Manchu Massacre would be just too handy a club for anti-religious polemics. Dawkins will have at least a chapter on it.
One caveat is that Hong Xiuquan himself didn't seem to care much one way or the other about Western science.
About Western science and technology specifically I think you're right. But if I recall he was hungry for Western approval and open to Western ideas in general.