I shop at a local farmer's market, and one of the vendors specializes in peppers. One year she had a variety called "sugarchile", which was as you described, sweet and flavorful, hot but not overbearingly so. They were absolute wonderful, I froze a lot to use during the winter and I never tired of them. I tried to grow them myself the next year, but had trouble finding seeds, as did the farmer--apparently there was a crop failure. She couldn't locate them for the next few years either, so my guess is that despite its wonderful taste characteristics, it was too much trouble to grow/hybridize, and has been dropped from commerce.
This year she is offering a pepper called "Crimson Lee" (not sure of the spelling) which comes close to "sugarchile". It is perhaps a bit hotter; when I bite into one, I start to panic, then the heat recedes quickly and I'm left wanting more. It's shaped something like a Hungarian semi-hot, but more narrow.
Cheers, Sue