Bittorrent isn't at all what you are describing, when. Peers are gossiping they are not sharing an ever growing dataset, it is a static file, and if it was a changing data set they would necessarily be discarding portions of it because they don't have infinite storage. In fact most seeders Immediately delete the static data as soon as they are done with it.

You can try to slow down the data growth as much as you want, but the best you can do is make it as expensive as a bitcoin transaction and make it take half an hour to hashcash an update, but ignoring the awful UX of that, the data still grows, forever.

How many nodes do you expect dedicating 100 gigabytes for that? Definitely not millions or thousands... definitely not as many as bitcoin nodes since it is not as profitable or necessary to store the full ever growing set.

And then these few nodes have to serve the entire Internet, and they become easier to control or attack because they are few.

You will never be able to have the full dataset, you will have to discard data, and the moment you start doing that, you will realise that people trying to read need to find out who has the parts they need, and they can't because there is no structure. So they will have to ask everyone, and that is exactly what a DHT is meant to make scalable; how to ask log20(n) nodes instead of n nodes.

Anyways, just build it, and see if you can survive spam without degenerating into a handful of nodes like an abandoned Bittorrent infohash.