All of us know that everything(Including the data we generate) on the blockchain has pattern and people who have been using bitcoin and ether complain that the network is slow. People often try to hard fork the entire network to combat this problem!.
Most hard-fork/chain-split to solve scalability problem have certain trade-off & most of people who do it don't care or never research the impact.
We are also on the brink of witnessing quantum computers which would prove very detrimental for the progress of blockchain.
Depends on cryptographic hash, signature or encryption. Few of them are safe or partially safe from quantum computer.
1. Could we write an algorithm to generate a consensus algorithm using the data
No, at most the data on blockchain could be used for consensus algorithm parameter/configuration (such as difficulty, reward, selected node to create blocks)
2. Is it anyway possible to merge two or three consensus algorithms together?
Yes, but depends on the consensus algorithm to be merged. The most popular is PoW-PoS hybrid.