Use case: ADA in the SL will be used for purchase, staking, voting, and a universal token that can be used as a medium of exchange for all others (at least that is what I get from the interviews that I have seen). The Computation Layer (CL) will be able to hold numerous different tokens in it. In fact, the ERC20 token will be compatible out of the gate with the ADA token. Unlike Tron or EOS, ADA is not an ERC20 token. However, developers will be able to bring their DApps that were constructed around an ERC20 token over to the Cardano CL. Due to their side chains research, other currencies will be able to be used on the CL as well. Bitcoin would be able to purchase a crypto kitty (or anything else) on the Cardano CL and utilize the low fees and high speed of ADA. When I also say voting, I mean voting for the treasury model, for countries to have secured elections, etc.
Speed and Scalability: Cardano/ADA plans to scale similar to that of torrent (the more popular you become, the faster your platform gets). Currently ADA is capable of doing 250TPS and it is being capped around 15TPS by the developers due to their not being a direct need to do more than that right now. However, it can be bumped to 250 very easily. Once the CL goes public, then the platform can grow organically to tens of thousands or hundreds of thousands TPS.
Sustainability: ADA plans on being sustained by their treasury system. There will be a small percentage (of the already small) fee that is taken and given to the Cardano treasury. There is where the funds can be voted on as to how they are distributed. Want to make an amazing DApp on Cardano? Sweet, publish your idea, and general business outline with how much capital you need to the treasury. Then the community will vote if they want to grant you the funds to build it for the community. There will not be a need for an ICO anymore and it will be much harder to fraud people out of their money. IOHK will also be publishing what they want to do research and accomplish on the treasury platform as well - and the community will vote on it. However, this will likely not take place until after the Goguen phase because the whole system needs to be established and growing before completely letting it go.
Liquidity: I guess I could take this two ways, the ease of extracting ADA into fiat soon, or the amount of money that cardano currently has to develop their project. I’m going with the former. ADA will be EXTREMELY liquid. The foundation is already working on getting ATMs set up in Japan and Korea for ADA and paper wallets are almost completed - it says 33% on the roadmap, but they are expected possibly in the next 4-6 weeks. ADA will also be, once again, designed as a universal token. This isn’t saying that it will drown out all other tokens, but that it will be able to just be friendly with the other hundreds of tokens that currently can’t talk with one another. This will all be able to be done through the Daedalus wallet. The wallet looks like it will be designed as almost a store for DApps to live in and users can choose which ones they want to use. Daedalus will also be used to move your BTC, ETH, LTC, or whatever into ADA. or your LTC into BTC (once again, that is just what I am getting from the interviews and I am not a developer for the company).
Decentralization: The goal is to have between 100 and 500 stake pools available for the community to choose from. The treasury voting would then primarily be done by these pools, but obviously the different countries elections would be held in a separate sandbox that would not be influenced by the general stake pools. Registration for test stake pools is going on right now and ends on 30 April. After that, they will test the staking in a closed environment to triple check for bugs and establish a sense of general UI. This will also give them an idea as to what else the community might want from the developers for the pools. Shelly will be released throughout Q2 and Q3 of this year. It is my personal belief that stake pools will go live to the public around July and smart contracts on the CL will go live around September or October. The DApps will be able to be developed in any computer language through IELE and IELE will take that language and translate it to PLUTUS. PLUTUS is the language for the ADA smart contracts.
If I got any or all of this wrong, I’m sure the community will let me know though. That too is something that I appreciate