[Moto G5S Plus Questions & Answers] internetpilot:
You calling it "moving on" rather than an upgrade is pretty accurate. It's an upgrade overall, but not as much as you might think for a 3-year newer model. You need to realize that the Nexus 6 was a $700 phone (when first released) and the G5S Plus is a $300 phone. The improvements with the G5S Plus is that it's 64-bit hardware, even though the stock ROM is 32-bit and most people highly suspect the Oreo update (if it ever comes) will also be 32-bit. Because it's not a Nexus, the G5S Plus has a microSD slot so you have the potential to have a lot more storage, but the camera hardware is not great (despite the fancy dual lens). The camera works out if flash a 3rd-party 64-bit ROM and use the Google Camera, but I can't do that (see below). On the US model there is no NFC, so no AndroidPay (I didn't care, but some might).

My personal experience with unlocking/rooting/ROMing the two phones has been very different when I thought it would be far more similar (since they're both Motorola). The best way to describe the process with the G5S Plus is kludgy, and it's not all that easy to go back to stock since there are no official, signed stock images for the G5S Plus. Stock updates (even security updates) are few and far between. This just isn't a Nexus. The Nexus 6 had a lot more 3rd-party development options and support, and the G5S Plus has now been out long enough that what you see here now is probably all we're going to get. I haven't had much luck with the existing 3rd-party ROMs working well with my carrier (Sprint). The ROM features seem to mostly work fine, but the carrier settings don't work at all on Sprint, and when I try to change them I completely lose my mobile signal and don't get it back until I reset network settings. This makes it highly questionable how successful I'll be with these 3rd-party ROMs when roaming, even just locally in the USA. I have no faith in these ROMs working when roaming internationally. The reason why I'm encountering the same problem with all of these 3rd-party ROMs is I'm pretty sure all of them are using the same base from the same developer. So if you're like me and have a problem with any of these ROMs, you'll likely have the same problem with all of them.

Overall? I wish I'd gotten the Pixel 2 XL. But although I can afford to pay $1000 for a phone, I'm not going to because that's just ridiculous. I've looked around...thoroughly. There just isn't really anything out there any better featured that doesn't at least cost $700, so I'm still using the G5S Plus. I may be a little more limited than you because I'm Sprint (CDMA) whereas people on GSM networks might have more options. I've had to go back to stock rooted 7.1.1, which isn't horrible but not really ideal (and not what I'm used to with the Nexus 6). But I can't successfully get the G5S Plus back to stock unrooted to even take security updates, so I'm on the October security patch. When the stock Oreo update is released, I don't see me being able to take that either. I'm hoping that development community here will put out a flashable stock Oreo ROM then, but then I'll still be in the same boat with OTA Oreo security patches. This is a very capable phone with some nice features, but if you liked being a flashaholic on the Nexus 6, I wouldn't necessarily expect the same experience on the G5S Plus.

FYI, I'm not a developer, but far from being a noob. I've been rooting/ROMing/modifying Android devices (HTC, Samsung, Motorola) since the Froyo days. I would have to rank this phone as the most difficult Android device I've owned to do all that.