I'm trying to understand how Praos accomplishes semi-synchronous consensus....However, even in this case, you're getting semi-synchronous chain growth, not semi-synchronous safety, as if there is a situation where a node accepts a block as finalized, and then network latency suddenly increases sharply (eg. it keeps rising exponentially), then an attacker chain could outgrow it. So it's not quite the same thing that you can get with traditional BFT-inspired algorithms...
