OK, well if he is insisting on an island, tell him the kitchen has to be larger to accommodate a wheelchair if needed. Heck, anyone as they age may need a wheelchair.
Second, if he is insisting on the laundry to be downstairs, that's fine too. All you have to do is create a space that can be used for an elevator if the time comes. Many builders will do this for you. They can work out a closet so that it can become the "chute" for an elevator if needed. Or heck, go all out and put the elevator in. It's much cheaper if you do it while building anyway. But if you decide not to, then mapping out where the elevator will go ahead of time saves time, money and hassle.
To be honest, if Jim and I were building we wouldn't even have a basement. We'd build out and create a rec room attached to the house on the lot.

The ramp we had installed, thank you to Ramp Up for the cost, was $23,000.

That's a whole lot of cash and one you may want to put toward not having a basement. An elevator cost even more.