They really messed up rapid adoption by changing the connectors for HDMI and, to a lesser degree, the USB and Ethernet ports, along with the USB-C power connection. All the older cases, and other devices, cannot be used with the Pi 4, unless one does some judicious cutting with a Dremel or some such tool, as I have done, and that will still be less than optimal. The Pi-Top laptop in particular cannot be accommodated in any reasonable way that I can see due to its more complex design for mounting the Pi's board and connecting the ports.
The HDMI connections are the bigger issue for most cases with its 2 that are micro form. The micro form would not be such an issue if there was only one in the middle of where the older full size connector was, but 2 of them needing a bit more space make it messier for dremel'ing, and about impossible to match up with existing displays that are meant to clip directly onto the board with the HDMI connector, and anything else designed for that connector. What were they thinking? Was there that much demand for connecting 2 monitors via HDMI? The existing HDMI and DSI connectors were not enough?
Now for those of us who are not good at hacking cases and connectors, we have to wait for newly re-designed add-ons and/or hack the interfacing ourselves with the potential of damaging the Pi 4.
Maybe the Foundation could bring out an "A" variant (A++ ?), that would just go with 1 full-size HDMI port, and at least lower the ethernet jack as many laptops have done to accommodate thinner bodies along with keeping the current A+'s lower profile by cutting down the the USB ports to 2 of single height, or even adopt the existing A+ configuration completely, although cooling clearances for heat sinks could be a problem.