There are basically four kinds of devices:
1. interaction peripherals where Bluetooth+batteries is workable (keyboards, mice)
2. interaction peripherals where Bluetooth+an external power cable is workable (speakers)
3. low-power data peripherals (CF cards, flash drives) where low-speed USB is acceptable
4. high-speed data peripherals and controllers (RAID storage, discrete GPUs, etc.) that effectively need a PCIe channel
1 and 2 are wireless, obviously. 4 doesn't get reconfigured much, so it makes sense that Thunderbolt and related "extension" ports are on the back of the device. (They were previously inside the device, after all.)
3 is the main problem, then, that currently suggests accessibility of ports: the small, transportable, label-able data-containing devices that descend from floppy disks.
But why not think of alternative solutions, if "lightweight" data storage devices are the only constraint?
One design I always thought fondly of was having small magnetic-backed data-storage "pucks" with no plugs as such, and making the non-screen part of the computer (e.g. the front-bottom panel area of an iMac) a magnetic attach-point for them. You would literally "mount" the your drives onto the computer. (Presumably it would inductively power them while they're there, too.)
This wouldn't be a very fast storage device class compared to something using actual wires, but it wouldn't need to be; fast storage is what Thunderbolt et al are for.
It'd likely also have other uses: for example, magnetically attaching your ID card (which is also a smart card) to a corporate computer to cause it to log in—and also to indicate to anyone else walking by that the computer is in use.