I would add the SPS in addition to witness rewards, but my next move would be to create a top quality suite of tools, SDKs, documentation, etc for various kinds of popular "dApps". So for example, if someone wants to build a blockchain-based game, they just grab the Steem Game SDK and it handles everything they need to build a game on the Steem blockchain - blockchain interaction, integration with tools like steemconnect/keychain, payments, token/NFT creation & management, decentralized marketplace functionality, RC/SP delegation, etc. Same for other popular types of dapps.
Then we go out and do whatever we can to get as many apps built on the Steem platform as possible, which should be a whole lot easier if we have great tools, docs, and support. Every app on the platform will need to hold enough Steem Power to support their user base through RC delegation, so if we're even remotely successful in getting some serious apps on here the demand for STEEM should quickly be able to outpace the new supply (due to significantly reduced inflation).
SMNFTs (Smart Media Non Fungible Tokens) or second layer?
Second layer.
This the best way forward: a full suite SDK for DApp developments.
Steem should not be used for rewardpool. SMTs with DApps can take care of it. Scot based @steem.leo, @sct, @palnet, @sportstalksocial have already proved it. Moreover, it is simple, for example, there is only LEO token: no LEO backed dollar, no LEO power, even all rewards are paid in 100% liquid LEO. DApps can play with their own reward pool distribution algorithm and find out strategy for own onboarding. Moreover, success will depends the DApp's developments. Investors and creators will move to the appropriate and successful DApp. It will be plethora of DApps, the fittest/best DApp/SMT will come out. Successful SMTs will drive Steem's price too.
@liberosist personal list of the ideas are best suited for Steem's future: https://steemit.com/steem/@liberosist/very-basic-stuff-steem-needs-to-fix-my-personal-list