Hello Sam - Not sure if you are also a member of the JMT Facebook group, but there is quite a bit of snow chat there. I've been posting periodic updates there of snow sensor data from near the trail for the past few years, and will do so this winter/spring too.
As a general comment on hiking the JMT after a big snow winter: it does raise some objective hazards (swollen creeks, steep snow, thin snow bridges, hidden hazards, sun cups, etc). I started my hike in early July 2017, a very big snow year, and all those things were relevant. Some people hated it and got off trail within a couple days. Others (like myself) just accepted the conditions and in the end I enjoyed the snow sections more than the dry trail. A key issue is that there's water everywhere, and wet feet becomes a way of life. However, there is a strange little window before too much snow has melted where the mosquitoes aren't that bad. I was amazed how easy I got off - a couple crazy bug sections but they were few and far between. Must have been either too cold or too much moving water for the bugs to hatch.
All that said, after big December storms it's been flat line for the past two weeks. Basically there is no telling how hiking conditions will pan out until April or May - in the meantime all the speculation is just for fun.
Lange Jorstad