Currently the fluid limit on dedigitization chests is set to 10k. Is it possible to make a setting to increase it?

That's just the volume of the physical fluid container, like storage tanks. What would be a reason to increase it?

Because it cant keep up with supply/demand with bigger bases.
I have a Foundry build that makes a few thousand molten iron per second and it fills up the chest very quickly, but I have a lot of chests so it takes around 15 seconds to cycle through and process every chest. I suppose I can add more chests to have a bigger buffer before digitizing it, but that would just make it take more time to cycle through the chests.

There is a startup setting for how many chests are processed per second, you can try increasing that to speed things up. Or you can edit the prototype yourself, it's in prototypes/digitizer-chest.lua, ctrl-f for "volume"

The mod was never intended to be used for logistic purposes, even though it has gotten a bunch of logistic related features added over the years. For the intended uses 10k volume is more than enough, so I won't be adding a setting for that.