That would be actually magic as the Favorites.plist file is only read right after launching the app 
Well, I am acknowledged by some to have special powers, but not with DEVONthink. Should have said, “on next open”. My bad. 
But as these files outside the database, is it risky/bad/don’t-do-it to sync these plist files? I fully understand not to mess files inside the database. Nobody should confuse that (although probably will).
The only risk is basically that updates of these files on one computer might get lost if there should be conflicts.
That risk covered as best as possible I think by
- let the computer do it in an automated fashion rather than manual
- use Chronosync which is supurb at avoiding and/or dealing with conflicts when syncing.
I don’t use Chronosync so I don’t know how it works but perhaps they could use an lsof and not replace the file when it’s in use.
Sounds like a bit of extra complexity to me …
As I’m using an intermediary location (the Dropbox folder, but could be any sync site) the Chronosync on each device is only comparing the version in Dropbox vs in the ~\library\application support\devonthink 3 folder. If the target file is “open”, then it either copies or it doesn’t, but eventually it will. Having a completely synched up Favorites list on both machines not at all a priority in my world. Just having them close to the same is better than always manually updating them.
That being said, I did a test. With DEVONthink running on the MacBook, I used finder to copy Favorites.plist into place from Dropbox. It copied. I did not do a lsof (too complicated). Yes, the Favorites list did not show up as updated until DEVONthink restarted.
Yes, probably not a perfect way to do this. Probably some scenario that you folks can think of before you implement some sort of Favorites sync … but for me it’s “good enough”.
Re Chronosyc working with “open” files, I can’t find any documentation specific to that question. But I have found Handling Conflict Errors in ChronoSync | Econ Technologies, Inc.