it's possible to enable wiredTiger encryption with inMemory SE

plavi@bender  ~/lab/psmdb/bin/percona-server-mongodb-3.6.8-2.0/nodes/db  ls -alh
total 24K
drwxrwxr-x 4 plavi plavi 4,0K lis   5 12:10 .
drwxrwxr-x 3 plavi plavi 4,0K lis   5 12:16 ..
drwx------ 2 plavi plavi 4,0K lis   5 12:17 diagnostic.data
drwx------ 2 plavi plavi 4,0K lis   5 12:10 keydb
-rw------- 1 plavi plavi    6 lis   5 12:10 mongod.lock
-rw------- 1 plavi plavi   93 lis   5 12:10 storage.bson

plavi@bender  ~/lab/psmdb/bin/percona-server-mongodb-3.6.8-2.0/nodes/db/keydb  ls -alh
total 16M
drwx------ 2 plavi plavi 4,0K lis   5 12:10 .
drwxrwxr-x 4 plavi plavi 4,0K lis   5 12:10 ..
-rw------- 1 plavi plavi 4,0K lis   5 12:10 key.wt
-rw------- 1 plavi plavi 4,0K lis   5 12:10 parameters.wt
-rw------- 1 plavi plavi   46 lis   5 12:10 WiredTiger
-rw------- 1 plavi plavi 4,0K lis   5 12:10 WiredTigerLAS.wt
-rw------- 1 plavi plavi   21 lis   5 12:10 WiredTiger.lock
-rw------- 1 plavi plavi 5,0M lis   5 12:14 WiredTigerLog.0000000001
-rw------- 1 plavi plavi 5,0M lis   5 12:10 WiredTigerPreplog.0000000001
-rw------- 1 plavi plavi 5,0M lis   5 12:10 WiredTigerPreplog.0000000002
-rw------- 1 plavi plavi  890 lis   5 12:10 WiredTiger.turtle
-rw------- 1 plavi plavi 4,0K lis   5 12:10 WiredTiger.wt

rs1:PRIMARY> show dbs;
admin      0.000GB
config     (empty)
local      0.121GB
ycsb_test  0.109GB

rs1:PRIMARY> db.serverStatus().storageEngine
{
        "name" : "inMemory",
        "supportsCommittedReads" : true,
        "readOnly" : false,
        "persistent" : false
}

rs1:PRIMARY> db.serverCmdLineOpts().parsed
{
        "net" : {
                "port" : 27017
        },
        "processManagement" : {
                "fork" : true
        },
        "replication" : {
                "replSet" : "rs1"
        },
        "security" : {
                "enableEncryption" : true,
                "encryptionKeyFile" : "/home/plavi/lab/psmdb/bin/percona-server-mongodb-3.6.8-2.0/mongodb-keyfile"
        },
        "storage" : {
                "dbPath" : "/home/plavi/lab/psmdb/bin/percona-server-mongodb-3.6.8-2.0/nodes/db",
                "engine" : "inMemory"
        },
        "systemLog" : {
                "destination" : "file",
                "path" : "/home/plavi/lab/psmdb/bin/percona-server-mongodb-3.6.8-2.0/nodes/mongod.log"
        }
}