Have you looked into level streaming? I have not worked with it that much, but it is designed to break up large levels, into smaller, more managable chunks. I mean let’s face if, 100,000 of anything is a lot of something, when your considering that there is the potential to have to look at each object (and it’s not like the system is only composed of the objects your creating) in order to draw the frame, and then a person wants that done, 30 to 60 times a second.
There is also LODs that can be done, to reduce the load, for drawing when seeing something from a distance. But I would highly suggest that you don’t need to have 100,000 ISMs, that the average screen size (1920x1080), cannot actually even display 100,000 decent sized objects ( 1920x1080 is a little over 2 million pixels, divided by your 100K, leaves you at 20 pixels per object, not very large objects to be sure.)
I would also suggest, on spawning, immediately around the player, as the player moves, things of this nature.