So is I-86 from the state line to I-81 now officially I-86 the whole length? I was getting mixed signals today taking I-86 on the way out to Michigan. I saw some plain I-86 signs, a TO I-86 sign near Vestal, and some only NY 17 signs randomly between Vestal and Waverly.
No. It's officially I-86 between I-90 and US 220 and I-81 though NY 79. There's still one project that needs to happen just west of Binghamton before we can have a Grand Unified I-86 (presuming nothing gets designated as a result of the current widening effort before that gets done).
If you are referring to the at-grade section east of NY 8, then that is east of Binghampton.
That appears to be the last at-grade section left.
There are lots of little things that keep the rest of NY 17 from being I-86 - not just at-grades. West of I-81, there's still one more project left. There's been speculation on what that could be on the I-86 thread, but it is known to be somewhere in the vicinity of exit 68. East of I-81, it's a lot of those little things (shoulder width, acceleration/deceleration lanes, interchange geometry, sight distance, etc.) that keep the upgrade from happening. That's why I mentioned the widening study - if I widening project were to result from that, a good chunk of the remaining work would get done (at the very least Middletown-Harriman, possibly Monticello-Harriman), and if that happened before the remaining project west of Binghamton (which doesn't appear to have any momentum, unlike the widening study), we could have a third section of I-86 designated. There are even covered signs around Middletown, the paperwork just wasn't submitted to sign it for whatever reason.