Haven't been keeping up, but considering how all the latest works (well, everything I've read, which hasn't been much lately, TBH) depicts Sidious as a nearly all-knowing intellect behind everything up until his death.
I don't see anyone surpassing him, TBH. The new big bad may present a more personal level threat to the main characters of the OT than Sidious did, however. Kind of like TDK's Joker was to Batman, whereas Ras and his organization was to the world. Joker would also get his head kicked in in a fight against Ras, but he still did more to Batman on a personal level.