Xi and Li Keqiang belong to rivaling factions. If Xi had his way at the beginning of the 19th Party Congress, Li would've been removed from his post. As a result Xi worked around Li where almost all of the State Council's functions are exercised by Offices and Leading Groups at the Central Committee level. Both Li and Vice Premier Hu Chunhua, who also belongs in the same faction, have been relegated to ceremonial duties and have limited to no say in formation of policy. For example Hu is 3rd ranked Vice Premier on paper and out ranks Liu He, who is 4th ranked Vice Premier. However in reality Liu has a significantly larger portfolio than Hu does, as he leads the Central Financial and Economic Affairs Commission... In essence Liu has been acting as Xi's finance minister, head trade representative, and economic architect. That is very much the reason all these Western think tanks come up with far fetched wet dream publications about how Li-Hu could lead a coup against Xi. As such it really doesn't matter who becomes Premier in the 20th Party Congress, because the State Council has seemingly become an empty shell (as in they're more involved with policy execution rather than it's formation) under Xi. Hu could very much succeed Li as Premier at the end of this year, but he'd only hold a title with limited to no power. With the Politburo and Central Committee heavily stacked with Xi's allies, Li or Hu would see almost 0 chance of occupying the top job.
Moreover, there is historical precedence from the 15th Party Congress where an out of favor Premier, Li Peng, who was age eligible to stay on the Standing Committee manages to keep the number 2 position whilst taking on a "demoted" post (Chairman of the National People's Congress). Zhu Rongji would become Premier whilst becoming 3rd ranked member on the Standing Committee. Although I'm leaning towards Li stepping down from the Standing Committee, I could Xi keeping him on and making him Chairman of the NPC as a sign of gratitude to Li for not outwardly challenging his authority.
While Ding Xuexiang does not have any direct governance experience, he has been Xi's de facto Chief of Staff - he knows the ins-and-outs of the Party and the ongoings of the country. I could see him replicating the career path of Zeng Qinghong, who was Jiang Jemin's right hand man. When Jiang rose to power, Zeng (who also had no experience governing a province or municipality) was placed on the Politburo as Organization Department Head so that Zeng would promote members from Jiang's faction into leading regional and central posts to undermine Hu Jintao down the road. When Hu came to power, Zeng made the jump to the Standing Committee as Central Secretariat and Vice President. Jiang may not have been Paramount Leader any more, but his interests were represented by Zeng. As such I could see Ding becoming Head of the Organization Department to strengthen Xi's power base, and subsequently make the step up to Central Secretariat in the 21st Party Congress to secure Xi's legacy.
I'd also have my eyes on Chen Min'er, who is currently Provincial Party Secretary of Chongqing. Prior to it being clear that Xi would get a third term, Chen was linked as his successor. Moreover before moving to Chongqing, Chen was Party Secretary of Guizhou where Xi has a large power base (as in many people in Xi's faction rose through the ranks via Guizhou). Chen has no experience in the State Council and wouldn't be a good fit at all as Premier or Vice Premier, but I could see him making the jump from the Politburo to the Standing Committee in the 20th Party Congress as Central Secretariat. He would then be in a position to act as an "emergency successor" should Xi have to step down for whatever reason.
