Five years passed but finally I managed to code it myself
https://mods.factorio.com/mod/sushi-splitters

Just needed to wait for the 2.0.67 version with splitter circuit support.

A possible solution if no default function is available below.
Performance-wise a native function would still be preferred.

local quality_levels = {
["normal"] = 1,
["uncommon"] = 2,
["rare"] = 3,
["epic"] = 4,
["legendary"] = 5
}

function item_matches_filter(item, filter)
-- Check name ...

Does a standard function exist to check if an Item satisfies a Filter?

Given for example an item:
{name = "automation-science-pack", quality = "normal"}
and a filter:
{name = "automation-science-pack", quality = "uncommon", comparator = "<"}

I want to check if the item satisfies the filter and don ...

If you want to mod a splitter, you can mod it this way for me

SpaceXing the rockets back to a landing pad would be so insanely cool

Searching for a solution once again, but there just isn't an option to change splitter behaviour, is there?
TransportBeltConnectable Prototype / Splitter Prototype


Wouldn't that be enough ? splitfilter.png

Doesn't work with a 'rainbow' belt containing mixed contents.

Edits, thinking out loud ...

Here's a more sophisticated application. I have a 'rainbow' belt on which I put a lot of different items.
Upstream I only put items on the belt if they are needed downstream.
I create a 'request signal' based on chest inventory downstream.
factorio3.png
The 'Belt sorter' mod has some features to ...

Hello fellow Factorians,

I was wondering if a small addition to the splitter is possible. I use the splitter filter function a lot to get specific items from mixed belts but it takes quite a lot of tiles to put them back on. A toggle option like the one in the attached screenshot would make my ...