-Not user friendly enough Dapps for mass adoption/lack of network effect.
-Overtaken by a competitor framework for Dapps like Holochain which is not even a blockchain but is also decentralized in a different way.
-Massive controlling stake that centralizes voting is a situation that keeps occurring disproving that DPoS works long term.
-Other possible DPoS failures, like Facebook hunting down top 20 witnesses to avoid Web 3.0 (yes, very creative scenario)
Important to note, scalability is not an issue with the RC system, it is actually better for the price if HIVE is not a scalable blockchain. The more people want to use HIVE the more scarce RCs become and this is what will drive the price of HIVE up (aside from speculation). If however, the blockchain is infinitely scalable, then RCs will never be scarce and people will just delegate them for a very low return because of infinite supply. As HIVE scalability increases, the price becomes more dependent on speculation only. This would be good for the world(censorship resistance, internet currencies with SMTs) but would be bad for investors specifically in the HIVE token. However, different SMTs can have different tokenomics which can always lead to good opportunities for investors.