It couldn't work for historious. Your ability to store a cache of a whole page is based on the same safe harbour that Google use to provide their cache. Namely that you merely act as a cache and the page is unmodified in any way. Modify the page, and you no longer have that safe harbour, now you'd have taken content from elsewhere and re-purposed it to have affiliate click-throughs... you'd have no defence to copyright infringement claims.

Historious has to store and present the cached page unmodified.

Oh, no, not the cache. There's much more opportunity in the links themselves. You historify an amazon item to go back to it later, and when you click the link to go there, our affiliate tag is inserted. Besides, you don't look at the cache when shopping, you look at the links.

I already pushed an initial version of this yesterday, it leaves your cache alone, is unobtrusive and gives us some extra money as you normally use the service.

If it goes well, we can even think about removing the limit for free users!

That works, in fact that use is going to be fine.

For your size, you probably would benefit from just applying skimlinks as they would give you a slice of revenue that you're not tapping into.

Once you go beyond a certain amount of traffic, ditch skimlinks and do it yourself. They take too much revenue.