Interesting question. I want to hear it a little more.
1. What kind of information do you want to replace placeholder with?
2. What kind of user interface to input data do you expect?
3. When you replace it with data in database, what kind of data do you need?
I realized simple placeholder feature in "Extra Question Field" plugin. Newest version is V1.3.3. "Position on question page" parameter is added in V1.3. Screenshot is old ...