For me, the kind of "ukulele" that is most painfully missing is a baritone ukulele with a body size (and scale length?) appropriate for its tuning.
Some may say that it's "going over to the guitar side" - but I see LOTS of potential and uses for a baritone ukulele that has a body size and scale length closer to a classical guitar.
Classical guitars have a deep, rich tone that far exceeds baritone ukuleles (although baritone ukes on the other hand are punchier).
However, I don't want to learn how to play 6-strings and turn myself into a guitarist in order to get that tone.
So far, the only luthier whom I have contacted that has given me a solution is Earnest Instruments.
But I've been quoted $2500 minimum, depending on options.
I'm looking for something a bit more mid-range in price..
If someone decides to produce this kind of ukulele, it's actually very easy and potentially inexpensive (just put a 4-string neck and headstock on a classical guitar body).
However, as such a standard instrument does not seem to exist...