Major - P3 mongostat run against a mongos with a --discover should show stats for the shards.
Legacy tool:
[gabriel@localhost mongo2]$ ./mongostat --port 27017 --discover
connected to: 127.0.0.1:27017
insert query update delete getmore command vsize res faults netIn netOut conn repl time
localhost:27017 0 1 0 0 0 1 262m 8m 0 109b 893b 2 RTR 14:59:36
localhost.localdomain:27018 no data
localhost.localdomain:27019 no data
localhost:27017 0 0 0 0 0 1 262m 8m 0 62b 733b 2 RTR 14:59:37
localhost.localdomain:27018 *0 *0 *0 *0 0 2|0 0 80m 487m 35m 0 local:0.0% 0 0|0 0|0 120b 3k 4 14:59:38
localhost.localdomain:27019 *0 *0 *0 *0 0 2|0 0 80m 487m 33m 0 local:0.0% 0 0|0 0|0 120b 3k 4 14:59:38
localhost:27017 0 0 0 0 0 1 272m 8m 0 62b 733b 2 14:59:38 RTR
localhost.localdomain:27018 *0 *0 *0 *0 0 1|0 0 80m 487m 35m 0 local:0.0% 0 0|0 0|0 62b 3k 4 14:59:39
localhost.localdomain:27019 *0 2 *0 *0 0 1|0 0 80m 487m 33m 0 local:0.0% 0 0|0 0|0 62b 3k 4 14:59:39
localhost:27017 0 0 0 0 0 1 272m 8m 0 62b 733b 2 14:59:39 RTR
New tool:
[gabriel@localhost bin]$ ./mongostat --port 27017 --discover
insert query update delete getmore command flushes mapped vsize res faults locked db idx miss % qr|qw ar|aw netIn netOut conn set repl time
localhost.localdomain *0 *0 *0 *0 0 1|0 0 272.0m 8.0m 0 0 0|0 0|0 79b 733b 1 RTR 15:00:00
localhost.localdomain *0 *0 *0 *0 0 1|0 0 272.0m 8.0m 0 0 0|0 0|0 79b 733b 1 RTR 15:00:01
localhost.localdomain *0 *0 *0 *0 0 1|0 0 272.0m 8.0m 0 0 0|0 0|0 79b 733b 1 RTR 15:00:02
localhost.localdomain *0 *0 *0 *0 0 1|0 0 272.0m 8.0m 0 0 0|0 0|0 79b 733b 1 RTR 15:00:03
localhost.localdomain *0 *0 *0 *0 0 2|0 0 272.0m 8.0m 0 0 0|0 0|0 133b 786b 1 RTR 15:00:04