Metal Gear Solid 4: Guns of Patriots [BLES00246]

Also I am really interested how will you handle the flashback sequence. I imagine that will be one of the hardest things to implement.

What/why?

The game calls PS3's internal PS1 emulator to launch MGS1
AFAIK not even PPSSPP supports POPS.

So you'll most likely need dump of the emulator ie. ps1_emu itself and then make it work.

When the game finally boots to menu I'll try my save which is literally right before the flashback sequence.