Can I build a Dapp on Tagion?
In the classical sense: no. Tagion is optimized for token transfers and is therefore not equipped with a stateful machine. It is, however, possible to build smart contracts and run the transfer through Tagion.
Thinking out of the box: yes. It is possible to use stateless smart contracts, and they have to be compliant with Tagion. Ethereum supports state full smart contracts which makes it simple to write a smart contract that could be used.