Ah i see, that sounds doable.
Only I think it is not a very solid feature. You still have no visual reference of all the replacement you're doing.
I understand that this feature would be useful if you don't want to replace all of the results.
So I think if you want to implement a feature like this, it would be better to add a checkbox in the find results tab so can select the results you want to preform a replacement on. In combination with the "Find Next Result" key-binding you will have more control over the replacements you will be making.
Then you can use the key-binding to visualy loop over the find results and use the checkboxes to select the replacements you want to make (and if that action has its own key-binding it would be great ).