Seems to me these all related to very limited informations about Indo's military. Subs, sukhois, helos, UAVs, corvettes, local LAVs, and others have already in list to develop Indo's military capabilities which since '98 has turned down.
Why subs? well, it will needed as striking force much as destroyers fregates, corvettes, FACs, etc. Nobody want war but all military in the world will think the same: hope for the best, prepare for the worst, right?
that's why countries in the world keep developing their military capabilities as far as they can, including Indonesia. And for Navy not only subs, there're also vessels for patrol in the list. Locally built PC-36 and PC-40, totally around 12-15 PC has been made so far and goes on. Also LPD from South Korea, 1 ship operational (need 5 of them, 2 may be built locally))for supporting force. Yes, eventhough lack of fund, Indo keep trying to build their defence posture that suits to its geostrategy and goepolitics.
Btw, Indonesia has no defence pacts with any countries so if 'something' happened in the future, who willing to help if not herself?
All those procurements already planned as in long term defence development for Indonesia's Navy from 2005-2024 as green water navy. You can check it (too bad no english section) in
http://www.tnial.mil.id/renbang.htm