To sum up - a complete waste of time, due to the company's unprofessional interview process conduct.
From the initial application, to the onsite interview, it took about 5 weeks. Spoke with their HR person first who was pretty accommodating, then had a phone screen with a principal engineer, then was brought onsite, where I spoke with him and 3 other people. This went reasonably well, and was pleasant enough to include lunch.
A few days later I hear from the HR admin that based on the interview feedback, they would like me to speak on the phone to two additional people (one of whom was their VP I was supposed to talk to in person, but wasn't available at the time). The second interview would be another technical discussion, which I assumed would be the tiebreaker of sorts, or the "bar raiser", in Amazon's terms. Then the day before the scheduled calls, it turns out the VP is still not available, so they inform me they will make their decision based on the outcome of one remaining phone conversation.
The phone call was completely not what I was expecting. Instead of speaking with someone who knew where I was in the process of interviewing with them and was intelligent enough to run the interview having in mind this was the final stage, they had me talk to a combative grunt-level engineer who works out of their California office. He was genuinely surprised to find out I had already been onsite, as he was under the impression this was going to be an initial phone screen. He started picking on the words I was using (e.g. attempted to debate with me what constitutes a distributed system), was fully unprepared to get the kind of solution to his coding exercise that I gave him as he struggled to understand it, clearly indicating lack of comfort reading source code, and generally didn't seem to care for interviewing me in general.
As if those alone weren't red flags enough, after waiting a couple of days after the phone interview I attempted to first contact by email the HR person requesting the status, then another couple of days later the principal I initially interviewed with, then just called the HR person a little bit ago and left a message.
Crickets.