Probably the worst thing you could do to this app is collect a bunch of features from us and start implementing them -- if you do that you'll probably add priority, user assignment, better authentication, sub-tasks and eventually be like the 1000 other shared to-do lists. If this is the direction you think is best -- probably it would be better to abandon this idea.
A different way is to keep doubling down on what you have --find a use-case where your perspective is required and all of those other things are not -- move very quickly along that vector until you have something that might not even be described as a shared to-do list.
Here's an idea of what I mean. This site seems well suited to ad-hoc teams, probably distributed (not sharing an intranet for example), informal, low-security conscious -- meaning their data is either public or they don't care if it becomes public. Perhaps short-lived -- definitely unregulated.
For this -- I'd consider to-do lists to be done -- what else does this team need? Apply your template (easy sharing, minimal, etc) to those: wiki, document store, schedule. But, always, always do it in the style you have here or even a more radical version of it (if possible). If no one wants that, then consider that there's no market for this.
But before doing any of this, I'd start measuring engagement and then getting yourself in front of the highly engaged and figuring out what they are doing -- you learn a lot more talking to consumers (those that are consuming the product) than people like us.
As for monetization -- ad-hoc teams will be hard to get money from, but a SaaS style subscription for repeat users would be the standard way, I think. To-do list is free, but other tools are an additional cost.