以下のディスカッションでシスコ社員の方が、ISR4000でも show idbを元にインターフェイス設定可能数を確認できると回答させてるので、ISR4000やISR1000でも同様なのでは？とおもいました。
https://community.cisco.com/t5/%E3%83%AB%E3%83%BC%E3%82%BF%E4%B8%80%E8%88%AC-ios-ios-xe/cisco-isr4221%E3%81%AE%E6%80%A7%E8%83%BD%E9%99%90%E7%95%8C%E3%81%AB%E3%81%A4%E3%81%84%E3%81%A6/m-p/4174881
ちなみに、以下はISR1111とISR4451の出力例となり、旧世代機器よりもIDBのサイズは大きいと思うので、設定可能数自体は増えてると思います。
Router#show idb
Maximum number of Software IDBs 16384. In use 18.
Maximum number of Micro Software IDBs 49152. In use 0.
HWIDBs SWIDBs uHWIDBs uSWIDBs
Active 12 12 0 0
Inactive 6 6 0 0
Total IDBs 18 18 0 0
Size each (bytes) 4952 1936 3856 616
Total bytes 89136 34848 0 0
Router#sh inv
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
INFO: Please use "show license UDI" to get serial number for licensing.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
NAME: "Chassis", DESCR: "Cisco C1111X-8P Chassis"
PID: C1111X-8P , VID: V01 , SN: xxxxxxxx
ISR4451#show idb
Maximum number of Software IDBs 16384. In use 35.
Maximum number of Micro Software IDBs 49152. In use 0.
HWIDBs SWIDBs uHWIDBs uSWIDBs
Active 13 24 0 0
Inactive 11 11 0 0
Total IDBs 24 35 0 0
Size each (bytes) 4936 1936 3840 616
Total bytes 118464 67760 0 0
--- 略 ---
ISR4451#show inventory
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
INFO: Please use "show license UDI" to get serial number for licensing.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
NAME: "Chassis", DESCR: "Cisco ISR4451 Chassis"
PID: ISR4451-X/K9 , VID: V07 , SN: xxxxxxx
NAME: "Power Supply Module 0", DESCR: "450W AC Power Supply for Cisco ISR4450, ISR4350"
PID: PWR-4450-AC , VID: V02 , SN: xxxxxxx
