If the possibility for Twitter to become decentralized on the EOS blockchain exists, what are the point-by-point steps it should take to become a dApp? What will happen to their existing users, how will they even login? And what will happen data they have created - Tweets, Retweets, Images etc? Can they be moved to the blockchain without user involvement?
In theory, Twitter could move all their data to EOS, using the blockchain purely as a replacement for their cloud services. They have just signed a contract with Amazon Web Services to do just this, so it is unlikely they will be moving to EOS anytime soon. However if they did, the move would be invisible to their users, who would not even realise they had moved to blockchain based dapp unless they read about it.
Crucially, twitter users would not necessarily need EOS accounts for such a dapp to work. Unless twitter wanted them to for some reason.
The questions they would need to answer is whether EOS based storage:
- Is economically competitive compared to traditional cloud.
- Has sufficient reliability and capacity. Something they may need to evaluate after EOS has been live for a time.
- Data security. How to store user passwords and other sensitive data? BlockChain and IPFS mean data is available to all. All encryption will only last for a finite time until it is broken. This can be a problem even in data-centers and cloud storage providers, where access is limited to a relatively small number. Some combination of private/cloud storage, breaking data to store via EOS block producers into small encrypted chunks, may mitigate risks. Recommending users change passwords upon every upgrade to a newer encryption algorithm, even if the old one isn't broken yet, is probably also a good idea.
Edit Third section on security issues added to answer concerns of @leo-ribbero in comments.
Before an existing business built on the current paradigm of a centralized server can migrate to a decentralized backend, they are likely going to need to completely revise their business model. In the case of Twitter, the reason for the business to exist is that they are able to sell ads at a high enough margin to justify the expense of their business operations. In a decentralized model - where users have ownership of their data and some control over how it is used by advertisers - the entire reason for the business to exist shifts.
Content and accounts could theoretically migrate, but the business that manages them would need a pretty compelling reason to move.