This strikes me as a non sequitur.
No one built a business dependent on RSS except for people in the business of building RSS aggregators. No content provider was effectively shut out of the marketplace (of content providing) by the death of Google Reader.
My point was that anyone building a business on top of Messenger that cannot stand alone is, probably, in trouble. But that's always been the case regardless of the base technology. What apps can be built on Messenger? Content delivery, potentially. Random data connectors like weather updates or where's-my-package. How can those apps stand alone against a behemoth like FB or Google or anyone else? They can't.
The point, then, is to build applications that make use of Messenger, but are not replicable by FB. Facebook isn't going to replace my FLGS. So how about I connect my inventory to an chat app so people can ask me if I have something they want? It cuts into my spur-of-the-moment sales when people come in, can't find Settlers of Catan, but see Dominion and buy it instead. But it also gives customers a better experience, and me a better understanding of what customers want (I got 20 queries for Catan this week, I should order a few copies).
Now, if I build a business which connects shop inventories to FB chat, I might be in trouble. FB can tear me apart in a heartbeat by building a small-business-inventory-chat-bot. And that's the way the world goes.
Don't build a company on Messenger that FB can replicate. Build connections to other businesses. FB won't be a bank. FB won't be a restaurant. FB won't be an Amazon. FB won't be a local small business. FB won't be a caterer. FB won't be a plumber.
EDIT: I'm tired, and this came out poorly formed. I may write another response later that's clearer once I've rested and reread this.