Let's not say a billion people came to HIVE. Let's say 500,000 did. For one thing, unless they invested in and staked a lot of HIVE to begin with they wouldn't make much on their product (articles). And even if they did invest, it would still take some time for people to get to know them and want to vote for them. All that investment would seem to me to increase the value of HIVE.
And what if their was very little investment but still 500,000 new people? Only a few of those people would stay dedicated and put in the time and quality to succeed here. And don't forget, most of the rewards we earn here (at least half) are paid in HIVE staking.
Another question. Have you read the white paper? Does more people mean more blocks will be produced? Does HIVE have interest? Is there a certain amount of coins produced like Bitcoin and then a halving? How many HIVE will be mined before we've reached the final coin to go into circulation?
Just some considerations that fall outside the typical economic scenarios.
RE: Massive Hive Problem