I don't have "track ends" but here's my Alfine with track dropouts and disc brake, it's new Surly track dropouts so no need to move the caliper:

My Koga WTR came with a sliding dropout on the frame,
the dropout also carries the disc brake mount, so they move together .

In the engineering section there is a set of drawings for manufacturing a sliding dropout set.

Their design has a 20 degree slope to the slider , so bike weight tensions the chain,
when the 4 big bolts are loosened , and at that angle the rim brakes ,
It seems to me, dont move too much off the rim, to need re adjusting.

so if an IGH/disc brake set-up works with horizontal track drop outs, why is that when i was researching IGH/disc brake bikes, they all seemed to employ vertical drops with an EBB, sliding vertical drops, or vertical drops with a chain tensioner? it seems to me that the manufacturers have dropped the ball making the systems unnecessarily complicated. is there any kind of disadvantage to a track drop-out/IGH & disc brake set-up like you have that would make the bike manufacturers lean towards using vertical drop outs and other means for chain tension?

With vertical dropouts, the wheel always goes back to the same place relative to the disc caliper and the fender doesn't need to be removed to take the wheel off. My EBB is trouble-free. Set it once and haven't touched it since.

Disc caliper issues would be the main thing I've seen mentioned, primarily in the context of single speed 29er mountain bikes, but the principle is the same for IGH's. I believe that some designs allow for wheel removal/insertion without the need to adjust the caliper.

For me, horizontal dropouts are like a heavy bike. I need to ride a heavy bike so mere mortals can keep up with me. I use horizontal dropouts because I'm too good of a mechanic and I need more challenge in my tire repairs.

I have sliders, ebb and horizontal dropouts on several IGH bikes. IMHO, horizontal dropouts rule. No added complexity on the frame (and nothing to fail), only slightly harder to do a wheel removal (once the chain length is set, it sets wheel position in the dropouts). OTOH, what do I know, I'm a Bear fan and I still patch tubes

BTW, all the newer Surly frames allow wheel removal without loosening the caliper. I don't have to move my fender, not sure why that always comes up.