Another VIA/QMK/VIAL nerd, mostly with 40%'s (split or otherwise, Chiri CE and Mercutio being my favorites), I think the main things modern keyboards should flat out adopt:

1. Offer a layout that's swapped CAPS with Ctrl.

2. Split spacebar

3. Remapping on the board

The caps/ctrl thing is just so obvious once you daily drive it for a bit. I personally banish caps to another layer and think even on normal keyboards it'd be better on a function layer, but given inertia and people swearing up and down they NEED capslock in 2026, this seems like an easy compromise.

The split space just flat out gives you an extra button.

Most people hit space with one thumb or the other (and in shockingly consistent spots, I find i use the middle space of 3 key split, which is the 1u). That means the entire other half of the button is wasted real-estate and the thumb on your other hand literally or mostly does nothing.

The final one with on board remapping is where you can customize that extra space to be the function you want. I know some people who swear by tap hold, double tap, toggle, whatever. Even thought those are being yelled about in the comments here, whatever your flavor you can do, and you've got a button for it right there.

If you still want your standard "i need a button for everything layout" cool, fine, this changes nothing.

If one day you decide you want to at least try something new (and if you can already touch type i HIGHLY recommend exploring the space with something cheap), cool. Here's a leaping off point.

Personally, the epiphany for me was realizing during some testing that yes i NEED a numpad/function keys all the time. But instead of that being an argument for a fullsize, it was actually an argument for getting better access to another layer so my numbers/functions are under my fingers at all times (4/5/6 is J/K/L). About an hour after testing that I never wanted to go back, and it feels so much slower and arduous when i'm not on one of my boards (god especially things like vim which love their escape key)