thx luca.

Yes, USB Host would be pretty. But I'd hate to have to hack my IT, fumble along with some sinister settings, bathing my hands in the digital guts. So it will be only official and out-of-the-box solutions for me.
And still I would eagerly shell out more money for an BT adapter than for any BT builtin peripheral, like keyboards etc. Imagine, if the keyboard breaks, just replace it with another 5$ standard keyboard, plugged into the adapter.

So, I'm then still looking for a standard desktopsize keyboard WITH bluetooth, don't need foldable magic for my home.