obspy supports reading the timing quality (blockette 1001) from a miniseed file if this information is present. However, it does not support writing it, as far as I can tell. Is there any plan to add this feature or has somebody already done this?
currently not as this is a non-trivial operation. MiniSEED saves the timing quality per record and those can have different lengths thus one ends up with a non-uniformly sampled time series of timing quality information. Furthermore once a file is read with ObsPy and in the Stream/Trace structure it does not have the concept of records anymore. Upon writing one would need to know how many samples end up in each record - that varies due to compression - and then somehow decide what the timing quality for that record is based on whatever information present.
That information is usually available at the station/digitizer and thus written only at the time of creation of the raw data record.