I think it has to do with the market. As you point out, there are a fair number of 30 meter rigs out there, and 30 is a pretty good band most of the time.

The other WARC bands, however, haven't been open very much until recently. If the band isn't open very often, who is going to buy a rig for it? And if nobody's going to buy, why would I market it?

Of course, there's a little visious circle here - in the absence of rigs, there are few people on those bands, and even if they are open, it's hard to tell.

There are really precious few 10 meter rigs, other than those aimed at CBers. 15 is disproportionately popular because it's easy to come up with a combined 40/15 antenna. Of course, even on 15, the band seems to be only 'open' when there's a contest. Folks are so accustomed to the sunspot doldrums that now that the higher bands are open they still won't call out or look around.

At least on 10 we have the freebanders to let us know when the band is open :-))

As far as designing such a gadget - don't let ignorance get in your way! Take a look at some other good designs like the NC20 or the 2N2/40, and go step by step making each stage work on 17 (or whatever). Sure it will take a while, and you'll make a lot of missteps, but you'll sure learn a lot.

I'm currently working on a 20 meter version of the 2N2/40. I don't have the know-how (or the equipment) either, so of course I'm struggling. But I'm having a heck of a good time and learning a ton.

I heard a rumor that the master himself is working on a 15 meter single bander. That might be a good stepping off place for a 17 or 12 meter rig!

Don't say you can't, just do it! You won't regret it.