This idea is very simple. It's currently possible to define parameter "spawnedby" for mobs and it's really helpful. Similar feature, but for blocks would be really nice to see in "OtherDrops" plugin.

Possible use (example):

User want to define special drops for block of grass, sand and dirt - for example - it's possible to find some money or rare items while destroying this type of blocks. Unfortunately, currently it's possible to collect many blocks of sand/dirt, place them and destroying them reparately. With parameters like spawnedby: generator/placed/environment etc. it will be possible to prevent this situation, and it will give many new possibilities while defining other drops for blocks.

Unfortunately there's no "flags" on blocks that indicate how it was spawned. I have also considered this option and it might be possible to some degree in conjunction with a logging plugin - do you use a particular logging plugin?

I'm personally using plugin "HawkEye Reloaded" for block logging, but there are many other popular logging plugins like CoreProtect, LogBlock and possibly many others I don't know. If it's possible to do with logging plugin it's still very good news.