I'll start off by saying this is an interesting project; In the past I've supported why people have avoided going TCP/IP for every single device in the home but if they're able to make it work cost effectively and find a market of people savvy enough to keep their light switches functioning after changing from UVerse to Comcast to FIOS - then hey, more power to everyone!! Honestly, I'll consider the technology if we start seeing the integration possibilities.
That said, I want to add some technical info on Wifi - as that's an area that most people just don't seem to understand. The problem about the number of client devices really has nothing to do with the Access Point or the devices - it comes down to a problem with the 802.11 protocol in that it's a Carrier Sense technology. Here's a snippet regarding how it works:
Wifi is CSMA so every radio has to wait until it sees an opportunity to transmit (*Carrier*Sense*). The more radios, the more waiting. when you get past 30 radios, the wait time begins to take up most of the radio time. You might get 100 clients to connect, but as soon as one starts to transfer data, many of those radios are going to lose their connection. The radio doesn't matter, the combo of CSMA and the wifi standard adds up to this limitation.
With something like TDMA (many cell phones), each client device knows its timeslot and there's no collisions but with CSMA each device has to wait for an opening then try to jump in - think of it this way - in something like TDMA, everyone can line up in a circle and each one gets 1 second to transmit (example) - so everyone knows when their turn is and how much they'll get through; with CSMA everyone is trying to bum-rush at the same time leaving the radios and the clients to fight over who gets to make a connection and that overhead alone can end up taking down the radio keeping *anyone* from getting throguh.
It's not insurmountable - but the solution to this problem directly conflicts another common application - seamless roaming throughout your home.
The way you fix it so more clients can connect via wifi is by turning the power down making the coverage cell smaller and using more AP's - that in turn increases the density available. However, there's no real roaming built into Wifi - so say you make the cells smaller - great - your stationary devices like light switches wii's and TV's will be happy... but say you then connect to your phone to watch a youtube video - as you walk from one end of your house to the other, it won't seamlessly jump to the strongest/closest AP just to keep a good signal; in fact it'll try to hold onto its connection to the weaker signal until it just can't hold it anymore (dropping speeds, causing excessive buffering, etc until it finally loses connection) then it'll finally jump to the stronger AP... So fixing one problem will screw up the other.
This is the very core of enterprise wifi engineering and what we have to deal with on a day to day basis when covering a campus or venue that has to support dozens or hundreds of client devices in a given space. There are of course some commercial options that have trickery to make this more seamless - which is very necessary for things like VOIP roaming between AP's while in the middle of a phone call - but those solutions aren't practical for 99% of the homes out there.
All that said, if I were designing a wireless infrastructure to combat these issues and provide support for my 75-ish light switches plus outlets plus Security Cameras, Media Players, and other devices around the home - I would do a hybrid solution. I would probably put in a total of 5 AP's... I'd use 4 of them alternating between channels 1 and 11 in opposite corners of the home to provide complete coverage with minimal overlap (by turning the signal strength down) and use them for stationary devices - then I'd use one high-powered AP central to the home to provide access on Channel 6 for devices like laptops, tablets and smartphones that like to move around the house a lot and need to be able to roam as seamlessly as possible. I can cover my entire 4000sq ft house on one strong AP if it's placed in the right location (as I do today). With even a basic management solution like the Ubiquiti Unifi solution, you can also set up multiple SSID's so that the main Channel 6 AP also can cover the stationary devices in the middle of the home but through the management software you can set it so the devices prefer to stay on the outskirt AP's keeping radio time maximized for mobile devices in the center. To be clear, there'd be one SSID that's on all 5 radios for stationary devices - then a separate SSID on the main radio for roaming devices that should reach the whole property (note: adding SSID's in no way allows more radios to connect; it's just a way to control what they connect to in this scenario - in fact, it adds to the beacon transmits that the radio must do which is also why even the best radios are limited in how many SSID's they support).
Again - this is me - but this comes from the experience of engineering large scale Wifi solutions - and it's one of the reasons I've warned that going Wifi for everything would introduce yet more technical challenges that are just too much for the average homeowner.
Seriously, ask anyone in the chat room, I have been saying for YEARS that this is what we need.
