Have their place, of course. For handheld devices, for example and today for most mobile devices. (It's not that hard to imagine, however, the availability of mass-produced directional self-aiming antenna systems for vehicles that are cheap enough to do away with omnis there.)

Fixed wireless should be directional, clearly. That is more work and a touch more expensive, but again it is the sort of thing that can come down in price. One can even make fairly simple mildly directional antennas without moving parts if you have multiple elements and can switch among them by electronic means. Expensive today -- but in quantity 100 million, almost everything is cheap.

Very small devices like bluetooth dongles and the like will continue to have omnidirectional elements, but at low powers and high bands, mostly.

Omnis can also make sense if you legitimately have a giant audience. If you have millions of people tuning in to a broadcast, using high-power, omni signals like a modern TV station is not selfish, in fact it's efficient. It is an interesting challenge to work out what the audience threshold is -- in this case we do have a scarce piece of bandwidth. To show you are not selfish in using it, you would just show that your audience is at some percentile of size.