I recently had a director reach out to me about joining their team to work on rebuilding an ad system from scratch, so unfortunately your fear may very well be valid.
Correct, they used to display regular ads on their website (but never in the actual games) for those users that did not purchase the Premium subscription. Users with the premium subscription would then see only user-created ads for user-created content.
It was honestly quite jarring and this new approach is better for developers on the platform, as they can reach way more people.
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.
exact opposite, they've made a 180 on advertising. there used to be external offsite ads shown on the website, which were removed. there used to be a developer API to show video ads for revenue within games, which was removed. they've cut down heavily on event promotions from companies (think movies that appeal to kids)
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.
