Electric tenor guitars are becoming a specialty of mine. They're rarer than 6 string guitars and there's not that many people out there building them, fewer still building electrics. Some of this comes from the lack of purpose built parts. I make my own pickups, but metal bridges are still an issue. In the long term I intend to come up with a tune-o-matic or similar type of bridge, but for now I'm mostly limited to a Fender style hard tail bridge for most of my instruments. It has 10.5mm string-to-string spacing and so is usually paired with an 1 1/4" or so nut which is my preference. I can make different string spacings and widths but it adds to the cost and I have to make the bridges.
There's a lot of variance in tenor guitars. Most of mine are 23" scale length, though I can build them with other scale lengths if you want. Plectrum guitars for instance are grouped in with tenor guitars but have a scale length similar to a banjo. A few common tunings are Cgda, like a tenor banjo, Dgbe, like a baritone ukulele as well as the treble strings of an electric guitar and Gdae, like a mandolin.
I attributed the recent popularity of the tenor guitars to an offshoot of the ukulele's resurgence, but it's not necessarily the case. Who's buying tenor guitars? Bass players, banjo players, dulcimer and ukulele players looking to expand, people trained on orchestra type instruments, Celtic music aficionados, frustrated guitar players, beginners and veterans alike.
So I've been getting into these lately myself, trying to build instruments that are both durable and somewhat affordable, the main ones I'm building on a regular basis being Standard and Scarlet.