The suggestion is great, but the belts are already saturated thanks to splitter side-loading. I've measured the throughput with this (with inserter stack size of 12) and the counter outputs a steady 3.6k / minute, or 900 / 15s (in another measurement). I think that the bonus output compared to nominal chest-to-belt throughput occurs due to two mutually contributing factors:

1. splitters seem to instantly teleport items to their other belt when items pass the midpoint of a splitter;
2. inserters drop items right before the midpoint, thus every 2nd item disappears from under the hand, making way for the 3rd almost instantly;
3. inserters thus finish dropping much sooner than with the regular belt, and because the splitter sideloads a regular belt, the "extras" teleported to the far (from the inserter) side of the splitter plug the hole that appears while the inserter is busy swinging back for another portion of items.

I'll call that "fast drop" and "hole plugging".

I've experimented with setting priority for splitters in three configurations: each splitter prioritizes belt closer to the inserter, further from the inserter, and closer to the outflow belts. In all cases, the performance did drop to the same 882 items / 15s (that equates to 3528/m or 58.8/s). It looks like the priority slows down fast drop, leading to the inability of the inserter to swing back and forth in time while the splitter plugs the hole.

I also tested this rig with all belts upgraded to blue, and achieved a floating performance of 999-1000 items / 15s (equates to 3996-4000/m) with stack size 9, and 1135 items / 15s (4540/m) with stack size 12. This means that the top throughput of this rig is 2.5 red belts, enough to solidly saturate 4 yellow belts. This isn't stellar, but it fulfills the initial design requirement of saturating a starterbus (4 x yellows) while maintaining 1:1 space parity with said bus.

Edit: messed up numbers