I want to share my research with the list that the OP gave.
1. Libra/Calibra
The target date is said to be in 2020 in the link below, but the announcement that they gave was June 18, 2019. So with all the news surrounding it about how it may not come to fruition is out of their control as said in the article. I think they knew that they would have a hard time to let the government accept it. There's no assurance that it would be released in 2020.
https://about.fb.com/news/2019/06/coming-in-2020-calibra/2. Bitcoin Halving
This is a sure thing, but there's no specific date. It would depend on how many blocks they would get. That's the reason why there are different times for different countdown timers by various websites.
3. Gaming Development on Blockchain
With the current uprising of eSports in the world, there's no doubt that Gaming Development paired with the blockchain tech is inevitable. I'm just not sure if there is a significant release in 2020 related to this. I think it still has a long way to come.
https://blockonomi.com/blockchain-games/4. DeFi Growth
This is the first time I have heard or read about this. Decentralized Financing is worth to watch out because of the possibilities. I just searched for it, but I'm not sure if it's the right one. Anyways, with events that are related to blockchain flourish, I think there would be a significant growth within the crypto community. I do hope that it would improve this year. That's what we need right now.
https://www.asiablockchainreview.com/projecting-defi-growth-in-2020/5. Central Bank Currencies
I just think that it's almost the same as fiat but in digital form or something. They want to create their own to have complete control. I think that's why we need more decentralized platforms to support the citizens of the world and the funds to be not corrupted. I'm not sure if CBDC's would be beneficial.
https://www.ledgerinsights.com/ecb-central-bank-digital-currency-cbdc-store-tier/6. Infrastructure and Web 3.0
The transformation of traditional businesses would something to watch out for, Web 2.0 to Web 3.0. Being able to utilize Dapps would be useful and a lot more. The semantic web, AI, 3D Capabilities, etc. This is the future.
https://www.trufflesuite.com/blog/how-the-arrival-of-web-3-0-is-transforming-traditional-business-models