The longest Im aware of is Knuckle Basses at 39". I know Carl Thompson has done a few 38" scales. My Dingwall is a 37" scale on the low B, down to 34" on the G.
And yes, the longer the scale, usually, the longer the neck, allthough there are things to do to maximize the space available. Longer scale also means the frets are further apart, and can be a greater reach in the low end. Some people with small hands cant get around that. Double bass is usually a 41-42" scale though, so if you can play DB, you can likely play any scale electric without too much hassle.