Somewhat related to smart splitters issues and normal splitter logic complexity on different types of belts connected.
There may be a different type of splitter called 'Counting splitter' where we may set on each exit how many items to pass there prior to switching to next exit.
This would mean though that it will work in waves especially when proportion is heavily skewed (like if you set exits to have 1-10-100, it will send 1 item to first exit, then 10 to second and then 100 to 3rd), but at the same time it will allow us to do compact splitters for weird proportions and do a predictable transport of merged items on one belt (still prone to overflow issues though as all other current splitters).
'Counting Mergers' may have the same logic - opening inputs in round-robin sequence for configurable number of items from each entrance.
I'd say this thing is to be higher-tier than smart splitters at least, may be on level with programmable ones (based on what we know about it currently) and below some future logic-controlled splitters/mergers if we will have it sometime in future...