It definitely doesn't mean ads, and introducing ads would be a mistake. They will likely lower the limits on free use once they're ready to handle a huge influ

It definitely doesn't mean ads, and introducing ads would be a mistake. They will likely lower the limits on free use once they're ready to handle a huge influx of paid users. They are in a tough spot temporarily ramping up things enough to take the limits of paid accounts, and since they can't onboard everybody they're being generous with the free tier, but that will end.