This is a great thread indeed! I came to using a threshold focused structure through lots of experiment and, seemingly, sub-par race results when I would include intervals faster than about 10km pace. It was in 2017 when I started to use the following structure:
Sun - AM: 60 min PM: 30 min
Mon - AM: 60 min PM: 30 min
Tue - Tempo Intervals (12*1K w/ 200m, 6*2K w/ 400m, 4*3K w/ 600m)
Wed - 90 min
Thu - Tempo Intervals (12*1K w/ 200m, 6*2K w/ 400m, 4*3K w/ 600m)
Fri - 90 min
Sat - 120-150 min (including 8-10 miles of tempo intervals)
For a period leading up to a half marathon and marathon, I would include tempo intervals in the Saturday long run as well. Typically in the form of 15 min + 6*1600m (or 3*3200m) + 60 min + 4*1600m + 15 min. I basically pulled this from Daniels' T-L-T workouts. After the marathon I was focusing on a 10km race so began doing the long run easy and did the Tuesday tempo intervals on Monday.
As has been mentioned already, I found the key to sustaining this was to keep the sessions controlled. I seemed to fall into a pace that was 0-5 seconds per km slower than my half marathon pace, so not true LT. This I think is key as if I tried to run my LT pace, I'd feel like I was reaching and would have not been able to sustain this structure. With the exception of the long run session, I'd finish the workouts feeling like I could have done more and gone faster.
The few times I broke this weekly structure was the Tuesday workout, ten days before a Saturday (or Sunday) race. For the half marathon I did 4*4K w/ 400m, for the 10k I did a 10km time trial, and for the marathon I did a 18 mile tempo at marathon pace (I did this on the long run two weeks before the race). The result, for me, was a PR in all three races, which were spaced six weeks apart. The strength that you develop and ability to recover between workouts and from races was most notable to me!
Also, I should add because I think it is important, my easy days were all very easy (i.e. no faster than 70% max HR, often under 65%). Hope that was informative and provides some further encouragement and insight!