The problem with these wifi based sensors is that you eventually run out of IP addresses (yes you could get fancy with subnet setup but still). Another problem is that at some point you might want to swap routers -- I had to swap out a faulty Netgear router, and the re-set was a major PITA. For these reasons I've been moving to Zigbee.
But your criticisms are strange. You have more than 254 devices connecting (which implies a complex setup) but can't increase the subnet size? Or does your router just have an absurdly small default DHCP range?
I also don't understand the swap your router problem, unless you're also using default SSIDs and not changing it. Configure the SSID and PSK to be the same as before and everything will just work.
Bandwidth and interference will likely be an issue far before ip scarcity.
What might be a problem is the number of devices that can be connected. For example someone who is using an Xfinity Gateway for their WiFi has a limit of 100 devices on each band (2.4 GHz, 5 GHz, 6 GHz) if they are on an XER10, XB10, or XB8. An XB7 can have 75 on each of 2.4 GHz and 5 GHz. An XB6 can have 30 on 2.4 GHz and 75 on 5 GHz.
That's enough for over 250 networked widgets to be concurrently connected with IPV4. That's a lot of widgets for one home.
If a person is getting into the realm of having a home with more than 250 networked widgets and addressing is becoming problematic in ways that are beyond their understanding and/or ability, then:
I might suggest that this is roughly equivalent to any other household thing that a homeowner doesn't fully understand (or that they don't want to understand), and that it would be completely fair to remind them that it is perfectly normal and acceptable to hire a qualified person or company to -- you know -- look into that for them.
(It's ok to hire a plumber, or a roofer, or a painter, or a cleaner, or any number of other professionals to help with making stuff work. It's also OK to hire someone to work on the network.)