I went on a nrrd binge and looked up some numbers. These do nothing to help out those that like longer necks but... If you take a 28 and 5/8 in neck and get the fret lengths, some odd things stare back at you. First up, If you subtract the distance of the first and the second fret from the over all scale length you get, you guessed it, 25.5 in. But subtract just the first fret and that scale length is 27.018"
Blah blah blah, what am I getting at. If you have to saw the fret board for frets, you already have the proper spacers from the 28.625 scale to make a ~27 in scale. You just need to engineer a neck that has a nice shape to it, and can retrofit into the 25.5 neck pocket. No biggie, right? Yeah, right... But, that being said, I have a 27" 7-string, an Agile Hornet, or King V. It is quite fun, and the lows are great. Big strings sound huge on it, piano like. You can drop it to A and it doesn't muck up, it just sounds mean.
I'd love it if Warmoth sold bigger length sevens, but I suppose the market is just not that big.
Patrick