Electronic – Very low wiper resistance Digital Pots – Anyone know of any

It looks like you have the SHDN pin tied to ground. The bar over the SHDN label means it is active low. This means that tying it to ground activates that circuit. According to page 20 of the data sheet you linked above, that will open circuit the devices.

"Both parts have a power shutdown SHDN pin that places the VR in a zero-power-consumption state where Terminal Ax is open-circuited and the Wiper Wx is connected to Terminal Bx, resulting in the consumption of only the leakage current in the VR."

Be aware of the capacitance to ground on each pin of the digital pot. The spec you embedded in your question suggest a range in the order of about 100pF. I don't know the exact switching frequency of your proposed application but, if it were 200kHz, 100pF would have an impedance of about 8 kohms (reactive) and this might be significant compared to the feedback resistor values you intend to enact with the digital pot. This could mean that you get a highly unstable circuit (worst case scenario) or, a lot of ripple voltage (more probable scenario) or absolutely no problem at all.

There isn't enough information in the LT data sheet to call this one so I'd advise setting it up with standard resistor values to cover the range you expect and testing it by adding 100pF caps across those resistors just to see if they introduce oddball behaviour. Other than that it should work just fine.

If it does got belly-up on you there is another alternative and that is to "offset" the feedback voltage with a current sink/source thus "conning" the LT8705 into thinking it needs to raise (or lower) it's mark-space ratio. The current sink/source can be controlled via the pot you want to use and because the pot would be "isolated" from the actual feedback node the capacitance problem wouldn't be an issue. Current sink/sources can be designed with very low capacitances (sub 5pF) so this should be OK. Remember, the standard feedback resistors won't introduce more than 1 or 2 pF and a bit of track might add another 2 pF hence my concern.