Now, if you were REALLY creative, you'd have an email client that would just grab all new mail and dump it into the Wii message board. You could have it priiloader autoboot it with just a "checking mail" message on the screen and then have it automatically return to the Wii menu when you're done.
I actually like this idea. How much do we know about the message board? I mean, essentially, it would just be an app that connects to your email, downloads new mails, converts it to wii message format, and posts it on the message board. Maybe use the SD card message signing that Letterbomb/Wiibrand uses? Then we wouldn't even have to modify nand, just download email and mark it read on the account, convert email to wii mail files, check mac, signs and send to SD in correct directory in the private folder for it to show up, boots wii menu.
Edit; the funny thing is, this system of creating your wii it's own gmail account and making a homebrew to fetch and convert mail on the fly is 10x more efficient than the Wii Message Boards intended use ever was. At least conceptually. Implementing it might be hard.
Another Edit; Going even farther, sending mail, you'd have to have the app check message board (meaning glancing and copying from nand) for memos (messages can't be sent because WC24 is gone, so that means no email validation or anything like that) composed by a certain Mii or something, convert to email... I guess the first two lines in each memo file would be the subject and recipient, and the 3rd onward would be the message.
The Wii menu would have to have some kind of "send/receive mail" channel, that would boot up, refresh mail, and then return to Wii menu with the mail refreshed.
To be honest, it seems like more work than anyone would be willing to do though, so i don't see it happening. It's a cool idea in concept, but ultimately useless.