"small" things like this I assume end up really expensive in wills.
Making a page of text available to the public for 500 years might involve 25 people (each person being responsible for 20 years), and each of them has to be paid enough to care. To ensure each is paid enough, there needs to be a fund to pay them, and that itself needs to be managed by someone, who will also want paying for their troubles.
Also consider that in 25 generations it's pretty likely there'll be a major war, civilization collapse, change of monetary system, etc. To make such a scheme resistant to such things, you're probably going to need multiple people involved in every generation, all geographically separated, and all will need paying.
Even if you set aside $1M of your estate to this, I don't give it more than a 50/50 chance of survival.
