It has been on the road map for a while but I admit the ability to configure global content from the templates is a new idea I hadn't thought of yet since the global content feature is relatively new. I just updated the work item in our project tracker to include notes about that idea. The basic plan is for it to be rather similar to what we already have for populating site content during installation. There we already have a system that allows defining content from xml files that will be used to populate the site content. I use this already to populate our demo site every time we reset it.
I'd also like to point out that currently if you have some sidebar content that you want to include in all pages you could put it directly in layout.master and then force it to show the side column(s), if you need it to be easily editable and don't want to hard code it in layout.master you could use ModuleWrapper.