Another service I use for massive collections of stuff is the social-bookmarking site Pinboard, which has a very simple but powerful API with a ton of third party apps.
Not only is it easier to find an app that suits my needs, but also I can easily build my own if I think it's worth the effort.
The developers of Dynalist are awesome for making a Workflowy-like app that is much-much more receptive to the community. But I say don't stop short there! Let's build a collaborative framework for listing and outlining together. I can't wait to see all the tools and additions people will come up with.