Cydia is no longer being maintained for iOS 11; we will be transitioning everyone to a replacement very soon.
Pwn20wnd, an Electra Team member, notes that "All of your old packages and your setup will stay when switching to Sileo!" and also confirmed that "Your Cydia purchases will also be accessible from Sileo." There will be a compatibly layer to handle all of the Cydia URL schemes and Sileo will be completely compatible with every Cydia package and repo.
In response to a "Cydia works seamlessly" comment, CoolStar tweeted that Cydia "only works because it has bandaids, zip ties and velcro applied onto it" and says that Sileo is designed for modern iOS and modern 64-bit tools.
Sileo will only support iOS 11. It is designed with modern iOS and modern 64 bit command line tools + libraries in mind. iOS 10 and older will not be supported as we won’t support using saurik’s 10 year old 32 bit tools with Sileo
Sileo will be bundled with the next versions of the Electra Jailbreak Toolkit. Please follow iClarified on Twitter, Facebook, Google+, or RSS for updates.