Yes, some people have had the problem with the 2017 models as well.
To the OP, here's my experience with my 2016 15" TB MBP, which has had its keyboard replaced just last weekend:
I ordered it as soon as they became available and received it in December 2016 and immediately started having intermittent issues with the B key repeating, but since I had to head overseas for several months I couldn't get it checked out right away. Like with yours, it was impossible to demonstrate it on command because it was too intermittent.
When I got back to my home country I took it to the nearest Apple Store (several hours away from where I live) and they couldn't see anything obviously wrong, and I couldn't reproduce the issue, so they "cleaned it out" and wanted me to see if it improved, but they also ordered in a replacement top case part (which as others have noted is what gets replaced when they replace the keyboard: the case, keyboard, battery, touch pad, etc) so they could replace it if it wasn't fixed. By the time the replacement top case arrived I was back home and it hadn't yet exhibited the issue again, so they closed the repair case but said I could re-open it later.
Fast forward a couple of weeks and I had to head overseas again (for a few months) and of course the B key started acting up, so I put up with it until I got back to my home country last week. I was able to schedule another appointment with the Apple Store, quoting the existing repair case number, and have them order in the part again in advance of me getting there. Down to the Apple Store (3.5 hours away), I checked the laptop in and they said they'd try to get the part replacement done that day, but it wasn't until the next day that it was completed, which was obviously quite inconvenient but 36 hour turnaround is pretty good in the scheme of things!
So now I have a brand new keyboard (and track pad, batteries, top case and I assume Touch Bar!), and the keyboard also happens to be the revised version that feels better, is quieter and has slightly different markings (it has the symbols instead of "alt" text etc on the control/option keys) and it's all behaving properly....... so far.
They did this for free, as they of course should since at this point it's a known manufacturing/design flaw. You shouldn't have trouble convincing them, but stand your ground if they try to give you the run-around, pointing out that it's the top of the line product, the expense, and that you buy Apple because it's supposed to be the best quality, and keyboards shouldn't have issues on $3000+ laptops.
