Hi Alex,
Thanks for responding!
AFAIK all crashes have happened while actively using vi, although I admit to being a little foggy on the circumstances of the first one or two incidents which happened maybe two weeks or so ago and took me completely by surprise. Since I started paying greater attention there has been no crash unrelated to vi.
Your suggestion about trying Terminal in recovery mode is a useful one, I can probably spend a certain amount of time doing that at some point this coming week. As noted, however, I could use it successfully for a solid day and more and that would prove absolutely nothing IMO, since my crashes are occurring roughly once a day at unpredictable times. If it did crash that might be a useful data point in the other direction, however, so that test could be useful.
I cannot justify the time involved with a full Sierra re-install, however. I have a lot of add-on software, local network configuration, etc., that would take me a minimum of a full day to restore. (But note that all of these mods pre-dated my upgrade from ElCap to Sierra and Terminal worked just fine under ElCap.) Furthermore, given that another user has already verified this problem on a separate, brand-new system, I see the chances of this solving my problem as being essentially zero. I'm a software engineer myself, and a SIGSEGV crash is virtually never due to anything other than buggy software -- it's fine to write an error message and consciously abort when a perverted operational environment is encountered, but a segfault is an outright bug and Apple needs to fix it.
If you haven't read the material in the other thread I mentioned to Sterling above and you are interested in following up on this issue, you might want to do that. John Henning, the other affected user, has been trying all kinds of stuff for ten days now to no effect, all of which is documented in that thread. If you are a moderator of this group you are more than welcome to fold my topic into his if that would simplify future communications.
Thanks for your help and please let me know if you have any other ideas! I will try the recovery mode test next week and report back, and am more than willing to continue to experiment to a reasonable degree to better define the circumstances under which the bug is triggered.
Roger