I don't know what Microsoft was thinking by having the base, performance or otherwise go dead on detach. It should still work as a bluetooth keyboard and the microsd card should be NAS. To conserve power, the NAS could sleep when not needed, as could the keyboard. Full shutdown of the base should be an option, but not the only option. Always half measure, eh Microsoft? Hololens with full display AR was too much to hope for too, I suppose. Maybe after we've gone broke buying the compromises you offer...... you'll do it right.
Microsoft was probably thinking...it makes sense and why would someone ever do that.
Detach the base just to continue using it as a bluetooth accessory? Your use case seems not all that practical. Disconnect the clipboard and what...find somewhere to put it? You'd have to buy a stand or something. There's no kickstand like the Surface Pro models.
And SD (not microSD, there is no microSD) card as NAS? What, over bluetooth? Slow. Wifi? Not the fastest but a lot more work would have to go into implementing that, which doesn't make sense when you can just attach to the base when you need the additional storage. I've not ever thought it'd be great if my built-in SD port would also double as a NAS.
I have a NAS. It's raid storage, fast, redundant, and plugged into my router and accessible to all my devices and provides services such as FTP, streaming, etc. as needed.
I guess I don't quite understand what you're looking for. A standalone Surface Clipboard with a bluetooth keyboard that doubles as a wireless NAS device? Because, that's not the Surface Book.
The base going dead on detach makes sense. It has nothing realistic to do, so why continue to waste energy.