With the advent of a few new kernel exploits for iOS 12, I decided my old "Should You Update to iOS 12 For JAILBREAK If You're On iOS 11.4.1/11.4?" video I made on August is no longer on point and needs some rectification. While most of the points I made in the old video still stand up, the situation has shifted a bit and although iOS 12 is still a very good choice if you really want to update, the real answer is complicated.
Some people may say: Why don't you say "yay" or "nay", why a five minutes long video? Well, the answer is not as simple as that. Yes, iOS 12 has kernel exploits available and iOS 11.4 / 11.4.1 do not. If you judge only by that then yes, iOS 12 looks like the heaven for jailbreaking, but a kernel exploit a jailbreak doesn't make. After that exploit ran and elevated your privileges or got you kernel memory read and write, it is the time for the post-exploitation part.
Post exploitation is a cumulative term which pretty much means everything else from sandbox escape, Codesign bypass, remounting of the ROOT FS, dropping the binpack, starting Jailbreak daemons and SSH servers and so on to running the uicache for Cydia to show up on the home screen. As you can see, there are a lot of processes in here and Apple can really mitigate quite a lot of currently used techniques for post exploitation. As far as I know, iOS 12 will come with some nasty mitigations and hardens a bit the self-signing so even though iOS 12 has a lot of kernel exploits lined up in the pipeline, the surprise that delays a jailbreak may be in post, where iOS 11.4.x have no major issues. Of course, there is also the posibility that the iOS 12 exploits work on 11.4.x but no word on that yet. See, it is much more complicated than a "yay" or "nay".