There is no indication that touch ID will be returning, as a matter fact, Tim Cook stated Face ID is the iPhone's future.
If the 2018 iPhone X Retains the stainless steel bands, glass, it will be likely the same weight or even slightly heavier for the rumored 6.5 OLED model. Regardless, this next iPhone will not be a major overhaul, it will be an incremental upgrade, because the newest form factor was just released this year.
It will likely look exactly the same (possibly new colors, though), be faster (A12), maybe have ProMotion and a faster Face ID (but we don’t know, it took 2 years for 2nd gen Touch ID). It will almost certainly have better cameras too (how much, we don’t know) and, perhaps, some specific hardware feature like a 3D camera or some laser focusing or something.
It almost certainly won’t have Touch ID or any changes to the thinness or aspect ratio.
Of course, until Apple announces it, it’s all speculation.