Hi!
One also has to be careful with qualifiers etc. For example, the start end end of a "spouse" statement should be copied to its symmetric version, but there might also be qualifiers that should not be copied like this. I would like to work on a proposal for how to specify such things. It would be good to coordinate there.
By coincidence, just today I was looking into "spouse" property's qualifiers, specifically start/end times - and we do have a sizeable number of entries where qualifiers on both ends do not match. Usually, the case is that one of them is missing, however it is possible to have them have different values - as different sources (especially after importing from different language wikis which may contain different information) may contain different values. We probably will need to have some way of manually handling such cases.
A first step (even before adding any statement to Wikidata) could be to add inferred information to the query services and RDF exports. This
Due to the above, automatic inference may be not trivial, especially for exports which are now processed in context-free fashion - i.e. each entity is more or less processed independently of others. There are also performance concerns - if when generating data about certain entity we will also need to load data about all entities it relates to, it greatly increases the workload per item, so we need to see if we can do it efficiently when doing dumps, etc.