Plain (non-wound) Bass Strings?
 

I'm curious, does any manufacture make non-wound bass strings? or at least maybe up to the D-string unwound? Or?

I'm curious because I'm thinking unwound strings may be easier to play because they are more flexible.

Heaviest unwound string commonly available is an .026, so unless you're using an extra-light set you're out of luck; I've also noticed that as unwound strings get heavier they tend to generate some oddball harmonics unless they're under relatively high tension and/or your scale length is longer than normal - somewhat manageable on a solid-body electric, but fraught with potential problems on an acoustic with its own unique frequency response and body resonances. FWIW back in the prewar/early-postwar era wound B-strings were commonplace on archtop comp boxes, there's a small underground movement among discerning baritone guitar players in the same direction (which I'm going to join next string change - the longer scale doesn't always help), and I've used a wound G on my electrics for the last 55+ years to improve tuning stability and harmonic consistency; IMO you might just be barking up the wrong tree here - I'd sooner be looking at one of the low-tension set options to provide easy fingering and consistent tone...

Unwound bass strings would be very stiff, intonate poorly and sound bad.

Just an uneducated guess. But it looks to me like, with a wound string, all the tension is on the core wire, not the outside wound wire. So a fatter core wire with nothing wound around it would have to have a lot more tension, no?

No. Tension is related to mass per unit length, string length and frequency. However the string would be stiff (increased resistance to bending) and sound bad and intonate poorly.