The way the sequels have been going they'll have Kylo kill a resurgent Palpatine, with the former turning back to the light, which would be a blatant rip off of ROTJ.
That said, I think it would work quite well to have the Emperor behind all of the First Order. It's well established that he was invested in the Unknown Regions, where the First Order grew strong, with the facility and battle of Jakku all engineered by Palpatine to ensure the Empire could re-establish itself out in the UR. He expended a lot of resources out there. Furthermore, the Emperor was also drawn to an unknown dark side force in the Unknown Regions, which could have well been Snoke; so it is not beyond reason that Palpatine was the real power behind this whole sequel trilogy.
In the Legends content the idea of Palpatine's spirit living on was also quite a popular idea - so that could explain how he ends up around again.
The trailer has made me a lot more hopeful for 9 than I was after the disaster that is TLJ. But, I'm holding my breath. JJ has suggested that there will be a lot of linkage between both the prequel and classical trilogies; there are rumours that the desert planet in the trailer was Tatooine, with Obi Wan's and the Owen's farmsteads apparently being used in filming. I also think it interesting that both the Episode I and IX trailers utilise "every generation has a legend."