I just do trails, not endurance, BUT, if you don't mind this from a pleasure trail rider's perspective, this is what I would love to see:
A selection of hoof boots (so I can see what they look like and how they work in person). I know not all endurance folks do hoof boots, but I always got the impression a good number of them did. (Is that true?)
And high quality mohair girths, well, that would tickle my fancy! I love anything mohair. It breaths and doesn't chaff the horses.
And a selection of reins that are trail-riding friendly. I HATE those itty, bitty, short contest/barrel racing reins. Useless on the trails! But I DO like one piece reins. Over 8 feet long would be great. I am currently using leather because that's all I can find pretty much over 8 feet. But like 8.5-9 foot mohair or other soft reins would tickle my fancy for trail riding.
I also love endurance style breast collars. I either make my own (usually out of used English stirrup leathers) or put a neck strap on my western breast collars. Still, western breast collars are often a bit bulky and really promote sweat. That's why I love the type endurance riders use, which are similar to an Aussie or English type.
Like someone else said, an awesome selection of saddle bags would be a plus. I love shopping for saddle bags and use them every time I ride.
And how about a good selection of helmets that are trail friendly? Nice and cool with good ventilation and in cooler colors. I live in the southwest, black is not a friendly color for summer! And helmet brims. I finally found one I like, called "Da Brim." I highly recommend them.
There are probably other things I am forgetting, but those are some of them.
I know bits are kind of personal between horse and rider, but a selection of trail friendly bits would be nice too. I know a lot of endurance riders use "S" type hackamores.
And if money were no problem a selection of trail and endurance saddles would be fantastic too! But that would be expensive to carry.
How about wool felt trail saddle pads? Another personal favorite. I ride western but I am BIG into wool felt saddle pads for trail riding.
Well, okay, I guess I've dreamed enough!