If the argument is, "It's on the blockchain for trust purposes!" my retort is, "Do you not trust the nonprofit? And if you don't, why are you giving them money?"
Please, do donate to non profits that align with your philanthropy interests, but don't get caught up in hype.
[1] https://helpx.adobe.com/acrobat/using/certificate-based-sign...
If I was going to donate a substantial sum to Watsi, I would wire it to them and have the wire receipt as proof of money transmittal.
For the features outlined before ("Verifiable donations, fully transparent reporting/auditing, no restrictions on who can donate"), for sure!
First you have to come up with a ledger you can run on your server, but that visitors should be able to verify that what your server responds, is actually the values, and that you haven't manipulated those values in any way. How do you even do that? Since you are running the software, you can modify it, either on the machine itself, or in transit.
Secondly, you need to come up with a way of avoiding AML/KYC since that or similar exists in most countries. You might need to hire a lawyer just in order to write the user-stories for your sprint.
Or, use existing software and boom, thing done. Publish and then circle jerk on Twitter.