WiredTiger update in KVstore is planned for a release some time in year 2020.
However, as mentioned by koshyk@ above, it would help to root-cause what usage pattern causes increase in storage space and if it is a valid use-case then provision/allocate the storage space for KVstore -- this is more of a sizing issue first and then a KVstore compaction issue, IMHO. Allocating required storage size via appropriate sizing should help prevent storage issues in the long-term.
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