Just a working idea, but after 3.09 here are some thoughts:

1.  Major Briggs not only saw details of what was to come, but as the ultimate good guy of the story, he is the puppet master that has lead the good guy team on the path of success.

2.  He was aware years ago that the good Dale was trapped and Evil Dale was loose in the world.  

3.  He faked his own death and hid out in some lodge/waiting room location in order to plan his strategy and wait for the right moment to act on it.  Likely aware that Dale would return and some point.  He was also aware of the creation of Dougie.

4.  He made sure to tie his clues in Twin Peaks to things the police of today could follow.  All in route to helping good in some way.

5.  He knew his body would be found and identified by the military and FBI.  Likely resulting to tie-ins with Gordon and his team.

6.  He swallowed the Dougie ring in an effort to aid the Gordon FBI team in finding the good Dale.  Not sure how or why he had it, but that was the reason for it in his stomach.

7.  If you take the principle at his word, and I don't, but if you do, Briggs ascended in the room and his head disappeared.  This would answer why you only see his head giving Dale a warning about the blue rose early in the season.  Which the clue itself is another example of Briggs' aiding other good guys.

I tend to remember hearing a story about plans for season 3, over 2 decades ago, that involved Briggs entering the lodge/waiting room and rescuing Dale since he was pure of heart.  This above set of ideas would seem to fit with a larger good guy role for a character limited today by the actors death.