The Raspberry Pi 3 Model B is a continuous development of its predecessor model Raspberry Pi 2 B.
Raspberry Pi 3 includes a 1.2GHz 1.2GHz 1.2GHz quad-core processor and 1GB of SDRAM memory.

Compared to its predecessor, the dimensions of the board (86x56x20cm), the location of the interfaces and the wiring of the GPIO pins have remained the same. Only the two status LEDs have changed their position, which is why they are no longer visible on one or the other housing.
Instead of the SD card slot with spring mechanism has entered a simple slot, where the MicroSD card just purely in.
Overall, this means that you can continue to use both housing and extensions in the rule.