Thanks for checking out the project pages and for your thorough comments, @John Broughton! I've learned a lot already from your input. I wanted to answer this one first before getting into the ones specifically about "structured tasks".
First, I just want to make sure it was clear that with newcomer tasks (which has been live on several wikis since November), we are not asking newcomers to place maintenance templates on articles -- rather, we are drawing on the existing maintenance templates to surface articles needing attention to newcomers. So hopefully this feature is a force for drawing down the backlog of maintenance templates, as opposed to increasing it. Indeed, I think a great potential outcome would be if enough newcomers were working through maintenance templates that it did make sense for more to be added by other users, starting a virtuous cycle.
One of the biggest problems with using maintenance templates for this project, though, is how open-ended they are -- we've seen newcomers who want to know which words should be links, or which sentences should be copyedited. That's why we're now talking about structured tasks on the other project page.
Another big problem with maintenance templates is removing them after the work is completed. The issue is that if a newcomer makes edits on an article after being prompted by a maintenance template, they probably don't yet have the wiki skills to understand templates and how to remove them. They also may not have the judgment necessary to tell if the template's need is entirely, or only partially, resolved. We don't yet have a solution for this -- perhaps we could encourage patrollers to look out for edits via this feature, and take a look at whether the template should be removed? Can you think of anything that would help here? Thank you!