It would kinda work for a general "block time estimate", but it would end up messy since blocks are ~10 min apart. If someone makes 5 posts in 10 min they're all going to show from the block. I'm thinking this roughly works only if each client showed the current block time too.

Honestly this is a BTC'er specific request and lots of people won't like it or find it useful. A block clock of some type would be required to know what the current block is.

I guess some clients could have the option to enable or disable?

I think I'd rather see the poster's time offset from mine, so I know if they're three hours ahead or working from the other side of the world. But that's probably not a great idea in some ways. hah.