X-Forwarded-For header?
Should cloud browser pass the originating IP address in the X-Forwarded-For header? archive.is does this: http://archive.is/faq
Do you preserve archivers' privacy? E.g. not disclose the source IP address?
Yes.
But take in mind that when you archive a page, your IP is being sent to the the website you archive as though you are using a proxy (in X-Forwarded-For header). This feature allows websites (e.g shops or the sites with weather forecast) target your region, not mine.
Came up in https://news.ycombinator.com/item?id=19349447#19351201, could be useful if abuse is a problem, but wouldn't be good for avoiding user fingerprinting.