Does this mean LA would be a feasible option for longer-cycle storage, IOW keeping a reserve topped up most of the year for those duldrums weeks with little solar or wind?

For long term storage, the right batteries don't exist yet (commercially). The good options are going to be one of sodium ion, flow batteries, or thermal batteries.

In addition to the fact that it doesn't really work better for that either, it's just not as safe as lithium iron phosphate.

I think it still loses out to lithium-ion on cost/kWh, and batteries in general are still a bit expensive for storage on the timescale of months.