There's no need to wait for the whole world to switch to a different email protocol. In fact, it's better if not everyone does so that spammers aren't incentivized to develop countermeasures. The use case is someone wanting to publish a contact email address on his or her web page. Your project involves writing some javascript code to do the proof of work in the sender's browser. You don't even need any cryptological expertise to pull this off. The javascript code can search at random for a token to be attached to the message such that the sha256 sum of the message combined with the token ends with a number of trailing zeros chosen by the receiver. More zeros mean more work.
The rest is just normal webdev stuff that can be as fancy or plain as you want to make it. If you have time left over, a server side filter written in any language you want to check the tokens would be nice.