What innovative, unconventional cartridge designs can you recommend?

"Unfortunately, it is far from the full story because the more capacitance you add for a given final voltage, the lower the ripple."  I think there you run into a law of diminishing returns.  Even if the relationship is linear and defined by a constant (of which I am not certain).  Regardless, you can easily see that no matter how endlessly you add C to reduce ripple, you cannot get it to zero just by increasing capacitance.  It will approach zero asymptotically.  Anyway, if you take a PS under load and look at the PS output with an oscilloscope, and if you can turn up the sensitivity sufficiently, you will eventually see ripple. The amplitude of the ripple V in relation to DCVout will give the S to N ratio of the supply. My earlier point was that there is little to be gained by using amounts of capacitance that yield a SN ratio much lower than the inherent noise of the system, although it makes for good bragging rights. Having said all that, I wonder why there is no proposal that I know about for a battery supply for the optical cartridge.  The current demand cannot be too great, and the battery can be re-charged between listening sessions. You could use a 6V battery and regulate it down to 5V.

You also wrote, "Thinking about reducing ripple, I wondered about using a Class A amplifier being fed a constant signal.  The output should be constant voltage, whatever the load."  Yes, but in TT speed control they use a particular frequency as the constant signal to drive the motor. For your cartridge, you want DC out; there is no need at all for such complexity. Furthermore, the output of the amplifier(s) used to drive the WB TT motor is subject to the same imperfections as those of a linear PS used to power the optical cartridge.

@richardbrand 

The difference in our set-ups is the equalizer. I was using the DS companion piece, and you have the SoulNote.

@lewm 

you run into a law of diminishing returns

Yes, that's what I wrote too.

Mindful that my SoulNote Equalizer has about 2 orders of magnitude less capacitance than some DS Audio ones, I note that SoulNote uses an active Darlington-effect ripple mitigation circuit, plus fast diodes.  This could get three orders of magnitude improvement.

The SoulNote keeps the diodes in my cartridge on, whenever the SoulNote is on, even if its source is switched to MM or MC.  The cartridge is warm to the touch, which will be nice in wintertime 

Like you, I often wonder why devices with low power requirements, of less than say 100-Watts, are not routinely powered by batteries. The house batteries in my motorhome can power my modest domestic set up for a few hours, but cost about A$10-k all up.  It would be cheaper if they directly provided regulated DC

@richardbrand 

My Umami Blue arrived today, along with the Soundsmith Counter Intuitive. I anxiously awaited the end of my work day and installed both the cartridge and the Smith. 

I’m blown away by the difference this cartridge upgrade brought to the table (pun intended). It’s simply incredible. Right out of the box it’s a major step up. I can only imagine what it will sound like after it breaks in. Super thrilled. 
Major differences are - more open sound, better clarity, mids are killer…vibrant, grainless and airy. Instrument separation, placement and focus are all several notches up. Soundstage grew in every direction. Noise level is significantly reduced. What shocked me is how much quieter it sounds even in dead wax! Barely any noise there. While playing no noise at all. 
I was running the ML at 1000 ohms load to open up the presentation. Umami Blue is great at 470 ohms. I’m leaving it all as is until it breaks in. 
So far I’m extremely pleased!