Midi input across two staves...

I (dis)like how you read personal insults in a mostly factual reply. Pointing out a way things currently are (and how the end result you're looking for can be achieved using those ways) is not the same as defending them.

So let's walk through the Pro's and Con's of your suggestion.
As you mentioned, it could make sense for a certain percentage of Piano music to use a split point during chord MIDI entry. The counter question then would be whether it would be counter-productive for those other scenarios: Cross staffed Piano music, multi voices piano music, other grand staff music (marimba, accordion, harp, organ,...). My gut feeling says that in most cases that indeed will be so.

The follow-up question then becomes, for most of those other scenarios; what is the effort/cost of fixing the input which might now be broken due to the split point. Moving notes between staves after the fact means cut and pasting them.

Your argument was:
"For example, an option that puts chords with their lowest note lower than middle c in the bass stave, or visa-versa. It wouldn't be perfect, but it'd make a lot more sense than having every note appear in the stave you select."
Except thus that fixing a wrong placed note due to this setting is more involved and harder than using the split point after the fact.

So what if we'd then make it optional? A setting somewhere to affect grand staff note input (or perhaps even just grand staff piano?) with a configurable split point. It'd give you what you wanted and other can just turn the setting off. My immediate response then is to wonder how much added value such a setting would generate you? And how it balances out compared to maintaining a special setting for it (and special casing note input for it). At this point, I'm less convinced about that tradeoff.
Because instead of getting a fairly short sequence of commands to split a staff (currently via the context menu) it'd now likely mean having to navigate through the gazillion settings to find that one (or two) setting(s) to en-/disable the feature and provide the split point. It also means I'd have to go there for every piece that uses a different split point. Or still use the current split command to fix things afterwards.

But that's just my view as one of the occasional contributors. Feel free to write out your "few minutes" of thinking this through to see how you'd evaluate the/those different possible use cases.

EDIT: RE "It's a shame there doesn't seem be a way to bring suggestions directly to those who are contributing coders."
There is, you're doing it currently. Here in the forum in the open. This is how you bring your suggestions to the coders and contributors. But then in addition you get the benefit (and so do the contributors) of the hive mind of users comparing use cases, possible pitfalls and/or voicing support for proposals.

As mentioned, there are such ways. Either enter the music then use the split staff function, or record the MIDI file then import that. But modifying the input functions to split automatically during input is complex, as i have tried to explain. Complex isn't the same as impossible, but realize only a very small percentage of users are inputting notes via real-time MIDI. So more effort is spent on areas of the program that benefit all users. And there are only so many people working on the program, and only so many hours in the day, Thus, so far, it hasn't become a high enough priority. But if one of the users ho does value real-time input were to volunteer to implement a good algorithm for this, no reason it couldn't happen someday.

On the chance that I'm saying what you already know. Here again the MuseScore way can do something similar, but as a two-step process:
1. Enter the full chords on the top staff
2. Use Tools > Explode to distribute them onto the other staves.

What this video shows is much more limited than what we assumed you were talking about. It isn't real-time, for one thing - it's still step-time. And thus it wouldn't handle the vast majority of piano music in which there are multiple rhythms happening at once. It would indeed be relatively simple to implement and could occasionally be useful for basic chorales, but actually, it was the entry into ensemble scores where it's much more likely to be useful. On the other hand, as mentioned, the existing split and explode functions handle this in just a few extra seconds.