Did it get taken down already? I think open-sourcing the algo would materially change the value of the deal.
Taken down by whom? It was posted on the official github account of twitter.
Twitters main value is its user base (especially including most journalists, "stars", politicans, companies,...)
I would say the algo itself is worthless, but my estimate would be nowhere near even 1B$.
If open-sourcing the algo allows bots to game the system then it has value to the bot wranglers; if the feed becomes full of garbage that gradually destroys Twitter's value.
Any worth that "the algorithm" has is not in it's implementation (probably pretty standard ML prediction systems), but in the training data and weights. In isolation from the data and the rest of the code it is probably pretty useless as anything other than an example of real world ML use.