It's the DM Notes feature that has proved something of an unexpected smash hit for the app, particularly among younger users, and the engagement benefits such text-based conversational prompts will offer have Instagram seeking ways to beef up additional elements into its core structure.

And, it appears, that could soon also be a move that adds Notes to user profiles themselves, with a new "Wall" display of notes being tested within the app.
IG is now testing a "Wonder Wall" display, which seems like a Notes display directly accessible from your main IG profile.

(I suspect "Wonder Wall" won't be the name IG goes with, but that's the tag it has now.)

This experiment appears to be an extension of a Notes display on user profiles, noticed last month, although the fact that users can seemingly add a note in-stream suggests it may be apart from your DM inbox Notes entirely, effectively providing the same functionality, but for individuals on their profile.
 Maybe.
(You're gonna' be the one that saves me)

I don't know, simply because the detail is still pretty limited-there are only a few screenshots of the option in testing, and no official word from IG on what, exactly, it is yet.

But it does seem like Instagram's trying to expand the functionality of Notes, which, as noted (sorry), have been popular among younger users. 

In June, Instagram said more than 100 million teens had posted a Note in the past three months. Teens are also creating Notes at a rate 10 times that of non-teens.

That's opportunity, especially as Instagram tries to hold on to younger audiences whose attentions are straying elsewhere.

That makes sense, with these users it would want to find even more ways to keep them engaged, and possibly, by having a prompt-based wall on people's profiles that other people can add something to-that could be a low-fi way to stay in touch, and keep the engagement going and going.
 
Even though, of course, you can imagine how it might potentially be misused-with bullies looking to post to people's wall to upset them, too. You would think, therefore, that users need control over the Notes displayed, though that would make it pretty much like DMs, right? Meaning they will become more public, but if you have to read and approve each Note before it's shown, what's the point? Answering questions for others to see? Organizing group meet-ups?

A bit anomalous, perhaps; but there is definitely a lot more to this, and we'll all find out as Instagram continues building out the feature.
Or it'll go away, and we'll never see it again. Either way, it's interesting to think about what types of engagement that Instagram is trying to promote with these efforts, and where this will drive future development.