Ironically, km/h is better for estimation because hours are 3600 seconds. If an hour were 1000 seconds or whatever, it would barely take more effort to calculate with m/s
Just leaving this here in case anyone is interested. A dozenal clock! Day (24h) divided to twelve parts divided to twelve parts, etc.
https://clock.dozenal.ca/
Seconds are already metric no need to redefine them.
Furthermore, if we redefine seconds we would also need to redefine a lot of other units.
This would result in massive confusion and a lot of avoidable errors in science and engineering, similar to what is already happening in the us with their bullshit freedom units.
It is not even that much harder if you get used to it.
If 86.4ks are too much to count for you, you could instead resurrect the metric prefix myria- for 10⁴. So 1day = 8.64 myriaseconds. And instead of minutes, use hectoseconds.