What I found out is that this thing wants to be in view_rss.
My patch supports basic cck fields (text, number, decimal, ...) and basically anything until you want to output text.
Html formatting can break things (for example if you're using multiple values).
This is a really simple patch, but doing a lot of functionality, if we want to support fields better we need wrapper functions with callbacks, but I think it's a good starting point.
I had only limited amout of time, but if you want me to experiment more you can contact my company Pronovix.