The maximum limit could be a mod setting. While a bigger limit would help, it would cause the number of items in storage to fluctuate wildly, making it not very useful for gauging if you need more production. I think there is some inefficiency with the distribution of items that needs to be fixed.
The current limit of 100k items would theoretically allow a transfer of 100k items per tick (6 million items per second) - which isn't being reached because of said inefficiencies. I'm pretty sure it's mostly an issue of how the processing order of machines isn't changing - for example, the same furnaces are being paired up with the same assemblers and the limit isn't high enough to hold the extra items for the next "chunk" of machines, causing items to be left behind.
