I think it would be naive to not imagine advertising as part of the long term strategy for a platform like this. After they go public, it's going to be a big tool in their toolkit for profitability.
they have an extremely high revenue business model off actual customers, so they don't really need to do advertising, there's plenty of other ways to get more profitable.
for example, they're at the scale where they might be able to do what Dropbox did by running more of their own infrastructure to save big.