A $1,000,000 donation is not practical.
There should be a special section for holders.
Why just for holders of x amount though and who gets to decide the amount and based on what? What makes you think there's demand for it as well? As I've suggested in the past I think there should be one or two new donation ranks though - just go with Gold and Silver seeing as we already have copper (maybe even a higher value one such as Diamond or whatever). Among the benefits of one of the pricier ranks could give you access to a 'hidden' board I suppose but not sure how eager people would be just for access to it.
And what happens if someone buys a Bitcoin to gain access, and then sells to to recover the cost?
Can't this just be applied to merit or feedback etc? Everyone will try buy their way around any rules or requirements if they can.