I'm mentally see-sawing back and forth re: crime of passion vs. a premeditated/planned murder, too.
The timing of her disappearance, i.e., her daughters being off on a camping trip, has me leaning premeditation.
Possible indicators of BM having an explosive temper, as evidenced by Gray Hughes' interview with JS on his YT channel, have me leaning crime of passion.
If it was a crime of passion, it's more likely that multiple mistakes were made by the perp.
In my mind, worst case scenario would be that there was a significant amount of planning done in advance.
If that's what we're looking at, then it's possible that someone took SM away from the home on the pretext of, say, going for a hike in a remote location, and then killed/concealed her at that spot.
Absent her body being discovered, LE is going to need a plethora of physical and/or digital evidence to reach the threshold of proof BARD.
I do not see an arrest being imminent in this case.
JMO.