All in all, if we escape the Submachine and make our way to freedom, if the outro music for Sub10 contains the four chords of hell I am automatically rating Sub10 0/10 >:P
But those pictures though. The resin temple connection made me double take.
1-5-6-4 is a very common chord progression which a lot of songs are based off of. It could be said between 80 - 95 percent of modern songs are based off that progression, of course with variations.
A double ending. One ending which is closed, another which sets the stage for the standalone games, the first being the engine. Maybe even an ending which sets up a continuation of the series, not a direct continuation, but a series set within the same universe.
Probably too far into development, but it would be cool of Sub10 could have it where, different items are used, to achieve one of those two endings.