The downside of floor drains is that drains are bidirectional and drain backups come out of the lowest point. That's probably ok in a laundry room or bathroom, but wouldn't be nice in other rooms.
Could you route the drains to plumbing lower down in the system? I'm picturing all wet rooms draining to a funnel in the basement via a dedicated gravity drain system. He did say 'custom home'....
Unless you're running a pumped drain system, all of your drains must route to plumbing lower down.
If upper floors' floor drains route to lower floors before joining with other plumbing on the lower floor, that would prevent backups from rising to the upper floor drains (unless their particular pipe was clogged, which should be unusual in a residential floor drain). But you'll have this issue at least at the lowest level of the dwelling.
Basements are not common where I've lived, but where present in custom houses, they tend to be fully finished and plumbed and then they'd have floor drains too.
In some buildings elsewhere, I have seen a less finished basement, with only laundry and a slop sink... That slop sink may be where a backup from the lateral to the utility sewer (or septic system) would come out. But that's not a common look for a fully custom home.
A lotta slop sinks are just washing machine drains. Lets your machine pump as quickly as it wants without needing to a separate high-flow drain. And buys you more litres of backflow before its a real problem. Tho some washing machines can pump up quite a few feet if needed.
Lived in an apartment where the front-loader managed to pump a sock into the high-flow drain where it got stuck. That was fun...
(Also had a front-loader break it's door seal, also a lot of fun...)
Even if there is a basement, a lot of homes will have a gravity sewer line that is above the level of the basement floor, and utilize ejector/sump pumps for water below the elevation of the sewer.
