That’s not a risk, that’s a remaining unsolved problem for blockchains in general (the balance between decentralization and throughput).
Solving the blockchain scalability issue by creating more blockchains makes no sense since limited supply is the very feature that makes blockchain unique.
Solving the double spend problem is synonymous with limiting supply (double spending is fine if you’re not trying to limit the supply of something).
[1] https://blockchain.info/unconfirmed-transactions