At this point, WPMU DEV has quite a few plugins that process payments (e.g., MarketPress, CoursePress, Membership, and Pro Sites). All of these plugins need payment processor information in order to work properly. On the backend, of course, this also means they all need the code to work with these payment processors. I suspect that there is some code sharing between the plugins, but there is probably also a good deal of duplicate code being maintained. For some gateways, having multiple plugins all requiring access to a single payment processor can lead to complications (e.g., having to configure IPN forwarding with PayPal).
Perhaps moving all of the payment processing under a single plugin would make things easier, both for WPMU DEV to maintain and for site managers to use. Essentially, here’s what I’m thinking:
Instead of having each individual plugin that needs to process payments have its own code for doing so and its own settings for configuring the payment gateways, a single plugin (perhaps WPMU DEV Payments) could be activated either at the site or the network level and used as a sort of middleman for transactions. This plugin would then handle all payment transactions required by other WPMU DEV plugins (e.g., if MarketPress needs to process a transaction, it makes a call to Payments, which then handles the payment gateway calls).
I believe this would make things easier for both WPMU DEV and site administrators (though obviously it would require some work on the part of WPMU DEV to create the Payments plugin and then to integrate others with it). Incidentally, it should also standardize the availability of payment gateways across different plugins (i.e., whatever gateways are supported by Payments would, of necessity, also be supported by all other WPMU DEV plugins).
Anyone who thinks this sort of plugin might be useful or helpful, go ahead and add a +1. Comments and suggestions welcome.