Hi David,
I had to go look to see that Gmail even had a spell check available anymore. I see it now digging into the "more options" at the bottom right of my compose screen.
I use the spell checking feature of my web browser to check my spelling. I suspect many other users do too since some of the major email providers don't offer spell checking anymore.
Is there anything about your spell checking that would be better than the web browser based spell checking already available?
Also, visitors might be more likely to "reply to this discussion" to get a notification when it's available instead of sending an email.
Good luck and let us know when it's available!