Re sleep states: while program is not suspended, the whole OS is. That's what keepalive is for. I suspect there is something in Jens's program which inhibits the sleep - should be keepalive.
Re suspend/resume media player: so, that means it player specific, isn't it? Which is rather poor design in my mind and should be solved on OS level (mixing players?). I guess we can do as others are, just implement it in platform-specific code.
Re blabbing/sleeping preference: the main risk is draining the battery of users who don't use this feature. I'd be cautious and add it under preferences.
Re closing PM and not being able to start: we had this issue earlier and never managed to track it down. is it on J1? No clue when was it discussed in this thread. Try to check if sailfish-qml is still running from prev invocation. I can look it up how to do that, but I'd prefer to continue with some other stuff. Maybe you can figure out the solution with ps and kill...
Re position marker without fix: its provided by OS and Pure Maps does not check anything so far regarding GPS status. Only things we get are position, uncertainty, speed. Direction, is probably calculated, but I don't remember correctly. [...]