Fasted training - is it worth it? Is it different when the focus is endurance? One thing I notice riding with an endurance-focussed club is that I need more, and more frequent, feeding than many of the more experienced riders. As I start to think about longer days (e.g. 400km) and consecutive days with a few hundred km each, I've started to wonder if fasted training will help. This would seem like a good time of year to start as I'm unlikely to do more than a few 200s before the weather improves, then I'll want to seize the chance to get the longer stuff in. 

I'm not trying to lose weight, but to be able to make better/earlier use of my fat reserves.

Recent cycling literature seems to be in favour of fasted training in the context of performance, but says little about endurance. There's general agreement that this is a fairly low intensity training ride but will take some recovery. 

The consensus appears to be that a 45-90 minute fasted session once a week is beneficial, and that's something I could build in to an extended commute. But does this hold true when the focus is on endurance rather than weight loss? Or do I need longer fasted rides? There are suggestions of a small calorie intake after about 45-60 minutes, or a little protein intake earlier in the ride. Does this change if the goal is endurance?
I'll preface this answer by saying i don't have any formal qualifications or education to answer this, but it is an area I'm particularly interested in, and have spent a lot of time reading about (and trying out in practice).

With the above out of the way, the short answer to your question is yes.

In fact, the primary reason to be undertaking this type of training is for endurance/performance reasons rather than weight loss.

Your body is perfectly able to burn both carbs (either stored glycogen, or from recent intake), or fat.  Burning carbs is easier, therefore, as you increase the intensity of exercise the proportion of carbs that are burnt is higher.
Fasted training is about teaching the body that carbs aren't needed, and that fat should be its preferred fuel source at low intensity.  By burning fat for energy, we are preserving our stored glycogen (and therefore energy levels) for longer.
By starting off in a low glycogen state, and not providing any more carbs, we accelerate this learning process, and very much replicates the latter portion of a long ride when our glycogen stores are getting depleted.

I experimented with this type of training (and continue to use it) with great success during 2017 as an attempt to improve my endurance before undertaking the NC500 route in Scotland.

You need to be disciplined to get the most out it, and stick to HR/PZ2/3.  It can be very dull, especially if you aren't used to it, and requires some advance planning to avoid prolonged steep climbs.  For your example of commuting to work, this would mean no traffic light sprints etc.

For me, after trial and error, I found this was more convenient to achieve by 'low fuelling' rather than dedicated fasted rides.  I would do my two interval sessions each week fully fuelled to get best quality.  I would do shorter endurance rides (up to 2hrs) on only water.  And for longer endurance rides I would ride the first hour on water alone, and then take half my usual carb intake for the remainder of the ride.

The process is very much like bringing yourself to the edge of a bonk in a slow controlled manner, without ever actually bonking.  For this reason, i'd always recommend taking a couple of emergency gels on these rides just in case.
It is often fairly unpleasant, with slightly increased breathing rate and a tired/lethargic feeling, but if things are going well, you should still feel you are applying the correct power to the pedals.