Ok, I had a chance to compare the behavior of my machine (9365) against another XPS 13 (9360) that works with STI/STR. tldr; suspend seems to work, it looks like resume works, but the screen does not turn back on.
STI
9360: Screen turns off, power button light remains on. Pressing the power button immediately resumes to original state.
9365: Screen turns off, power button light remains on. Pressing power button seems to have no effect. Pressing and holding power button for ~8 seconds the screen comes back on, original state is resumed (run level 3 it stays on, run level 5 screen immediately goes off again).
STR
9360: Screen turns off, power button light goes off. Pressing the power button immediately resumes: power button light comes on, screen comes back. Original state is resumed.
9365: Screen turns off, power button light goes off. Pressing power button, the power button light comes back on, but the screen remains off. Pressing and holding power button for ~8 seconds the screen comes back on (run level 3 it stays on, run level 5 it immediately goes off again).
Ok, I had a chance to compare the behavior of my machine (9365) against another XPS 13 (9360) that works with STI/STR. tldr; suspend seems to work, it looks like resume works, but the screen does not turn back on.
STI
9360: Screen turns off, power button light remains on. Pressing the power button immediately resumes to original state.
9365: Screen turns off, power button light remains on. Pressing power button seems to have no effect. Pressing and holding power button for ~8 seconds the screen comes back on, original state is resumed (run level 3 it stays on, run level 5 screen immediately goes off again).
STR
9360: Screen turns off, power button light goes off. Pressing the power button immediately resumes: power button light comes on, screen comes back. Original state is resumed.
9365: Screen turns off, power button light goes off. Pressing power button, the power button light comes back on, but the screen remains off. Pressing and holding power button for ~8 seconds the screen comes back on (run level 3 it stays on, run level 5 it immediately goes off again).
I'm attaching dmesg logs for pre and post STR.