Just an idea I had for my LTN Bob's/Angels Playthrough.

To use the full capability of the BRL with all the Bob's/Angels Ore Sorting, there has to be some sort of filter on the Export.
Otherwise the Train would fill up with everything that isn't required.

i.e. Level 1 Crushed Bobmonium sorts into 1xSlag/2xTin/1xSilicon.
Level 2 Bobmonium Chunks sorts into 1xSlag/2xTin/1xSilicon/1xCobalt/1xZinc
So I'd need to re-design another 2 Train stations otherwise.

Is this a possibility?

I will not add any filtering on BRLs. By concept they are gravity powered devices with a single large hopper that dumps indiscriminately into a top-loading wagon. You will need to filter before inserting into the BRL, and usually use 1 BRL per item unless you use a very sophisticated circuit contraption to manage the contents of the BRL.

This is the gameplay trade off for the BRLs’ large buffer size and speed: they’re dumb. If you want something smart, use inserters.

Can you add a circuit to read how much is in said loader so that I can add it to my LTN network?

It already does that.