Apple will probably never release a Watch SE with always-on display. For the normal Apple Watch, this is the major selling point, if not the most important. For me, it makes the device really 'feel' like a real watch. A quick glance at your wrist tells you the time from any angle, instead of raising your wrist all time. Coming from a series 0 to series 7 the AOD made a huge change (the most important one, apart from the expected speed bump). I'm all for power-saving things (never use AOD on my iPhone, don't like it there), but on the watch, I always have it on.
If Apple released an AOD Watch SE, there's not much of a selling point left for the normal/mid range Apple watch. I mean, what most people just need is 'watch' functionality and basic heart rate and gps (enough for most workouts). Most of the other sensors are in the end just a gimmick (for most people anyway). So when the SE has what is has now, PLUS an always on display, there's no good reason to upsell from an SE. For people only using the device now and then mostly for workouts, an SE is perfectly fine already, no good reason to spend much more.