@codenul What I can say is, that the pins at the bottom work for charging the battery (even if the battery indicator does not display the charging state).
I am not sure, if the pins also transmit any data, when Ubuntu Touch is used.
If I watch the dmesg output, while (un-)docking, I see messages like "pogo pin connected".
There are "Pogo pin Keyboards".
I think one just needs to try, if that works.
If not, a bluetooth connected keyboard would be an alternative.