I'm a new member of wpmdev and I have to say I'm quite impressed with quality of the plugins and themes. Supporter with its simplicity and functionality offered is quite amazing but I do think it need to have ONE major addition:
Credit Card Gateway support.
Even if it is only PayPal Merchant, which would allow majority of the people to use it. Although this would cut out many people from other countries who have no ability to create PPL Merchant account. So perhaps something different like Authorize.net or 2Checkout.com?
Just an idea that would allow Supporter to be a lot more professional grade. Reason for this is quite simple - many businesses are not into using PayPal and offering direct CC payment is theo nly option they are willing to work with.