Imho DPN, BTO, and REM are still relatively new and they will serve until at least next decade. The Parchims class on the other hand needs to be replaced soon.
And if it is combined with a swarm Underwater Unmanned Vessel a.k.a midget to add the blow by launching their torpedos from nowhere, it will be serious chaos. But this UUV proposed by PT PAL's new director is still far from reality by the way.
12 F15 EX are is not enough to replace the Sukhoi family, at least it should be the same number or more. Why do they persistent to offer viper while they know that the user wants super eagle?
It makes more sense and is simpler if PT PAL cooperates with MHI to produce a Mogami class than designing IH from scratch. The Mogami class is still new and the shipyards are still active in cooperating, and politically it has been supported even by the leaders of the two countries.
It is not surprising that PT PAL wanted its own design, considering that its President director was the founder of PT Terafulk design. He also has experience working in a shipyard in Japan.
I think $600 million for the second-hand interim submarine is too expensive. It is better to optimize the utilization of the existing submarine while waiting for the new one ready.