I use a synology NAS for time machine (time capsules are routers, and the poster was talking about an alternative to that), but your suggestion makes no sense for most people. If you have a MBP you aren't going to sit on the couch or walk around the office with an external drive plugged into it.
A much better solution for people who want time capsule support is, for example,
https://www.synology.com/en-us/products/RT1900ac. Just plug a drive into the router and you get time machine support.
If all you want is a mesh router, then you are probably better off with eero or google wifi, which look like they are more likely to be around in the long run than your suggestion (certainly google isn't going away).