another method for completeness that also uses math:
try to match the target water percentage
subtract water: weigh out pumpkin weight of (banana recipe grams of banana) * (.90/.72) and dehydrate to reach that weight
likewise for fruit with less water
if the substituting dried figs at about 24% water, weigh out
figs = (banana recipe grams of banana) * (.24/.72)
water = (banana recipe grams of banana) - (figs weight)
mash that weight of figs into that amount of water. with figs and water, finely chop the figs, add water, and leave covered in the refrigerator overnight for the figs to absorb the water, mash until it's a consistent mush, ends may not rehydrate, so discard any remaining hard bits
you're right on the other parameters
- between different fruits, there may be difference in acidity, as in pH not sourness, that will affect how much baking powder is needed
- sugar content can be adjusted similarly to the weight method above
here's the big one, though: flavor. pumpkin, like apple, is relatively a much weaker flavor than banana. to get the same amount of flavor, you'll want to add more pumpkin that's more dehydrated, but that will definitely affect the way you calculate the amount of water in your final recipe that will take some data gathering:
- how much weight in water is lost during baking a normal loaf of banana?
- how much more reluctant to giving water up is pumpkin than banana? (affects cooking time and temp, so cook to minimum internal temp, but at a lower cooking temp so the crust is still edible)
matching the flavor concentration of banana bread may not be achievable without seriously negatively affecting the texture of the loaf, so that's when you start to consider other ways to add more pumpkin flavor, like pumpkin flavor extract. but again, this sometimes leads to qualities that "just don't seem right" after you've smeared butter on a still-warm slice from the loaf.