If you call moveCollection and specify the destination using the url of the shard rather than the shard name, the resharding operation will hang.

ex.
 

assert.commandWorked(st.s.adminCommand({moveCollection: unsplittableCollNs, toShard: st.rs0.getURL()}));

will hang the test.

This is something we actually allow for movePrimary (see this test as an example) so I would expect this to work fine.