A desktop publishing application from Microsoft that focuses on page layout and graphic design.
I agree with the OP. My husband and I run a small IT support business in a rural area, and we have hundreds of clients that are going to be slammed by this, including a number of non-profits who rely on it for daily use. Canva/MS Designer type products just aren't good replacements, because they're so "smart" that they're stupid. Everything auto-resizes and auto-crops and auto-everything; elements do not line up neatly without heaps of struggle, you can't add grid lines easily for margins and folds, they don't have options for booklet layout, basic functions are limited (fonts, page layout/margins/formatting, bullet list options, tables, etc. etc.)... I could go on and on. Word is much too clunky and ornery for any serious layout scenarios; it's a word processor. I've heard it suggested that PowerPoint is a good alternative and I almost choked. Clients bring me brochures or handouts or forms that they're struggling to assemble in Word or PowerPoint, and I flip them into in Publisher in a matter of minutes, where they become robust and beautiful, and most importantly, easy-to-update for the client whom I've already converted to Office 365. I have over a decade of client and personal work files that are all going to need to be converted to who-knows-what format to try to save them, and scores of clients who will need training on some new platform in order to salvage their stuff. So far it's looking like Scribus might be our only option, but it's not a great option.
I'm all about starting up a campaign to see if we can get Microsoft to reconsider supporting this product. I own InDesign but never use it, because Publisher is sufficient for most layout tasks, much easier to work with, and I can hand my clients their own files to keep updated after I do the initial layout. This would be impossible with InDesign, which is even less user-friendly than an income tax form. I would rather keep all our clients in the Office 365 stack than start experimenting with open-source software.