@Carl Would this also work for the 3 way dimmer switches? The KS230. 

  @ScottMan can you please explain a little more in detail. My electrician and I are trying to understand it. Are you saying we need two dumb/sattelite (only 2 screws) switches and one master (3screws)? Are we to replace the the 4way with a dumb/satellite switch. If so, please explain a little more in detail. Thank you for your help and fguring this out. TP-Link should really fill this void out.

  @Mopy, that's right. Put the master in the box where your line comes in. The first satellite will have two wires connected to each screw - one being the traveler from the master and the other being the traveler to satellite #2. That is the case for both traveler #1 and #2. The second satellite has the load connected to the same screw as traveler #2 just like a normal KS230 3-way configuration. Hope this is clear.

I agree that tp-link should be addressing this. This configuration has been working great for me for about a month now - so I'm hopeful that it will be stable for years to come. I'm not sure if you can add more switches in line like this - like a normal 4-way switch where you can add as many as you want. I suspect that adding more will become problematic for the internal circuitry (as the switches are operating in parallel) and that is the reason that tp-link does not want to support this as a true 4-way switch. 

  @ScottMan thank you for your quick reply. I got it working. Everything works as should via APP and via switch. I simply bypassed the 4 way switch by wirenut traveler 1 together and traveler 2 together and went master Switch to the satellite #1 and put traveler 2 and load together  And traveler 1 on it own screw. (Like normal instructions) Then turned off breaker and undid the bypass I did and plugged in satellite 2 the same way as satellite #1. In parallel. I think your right and traveler 1 might be used as communication. My big confusion with your explanation was you mention you installed the them in serial. I got it working before I saw your post as I didn't think you would respond so fast. 

Anyway! Thank for your help! I wouldn't have been able to do it without your initial post.

P.s. I suspect it might work for 4 total switches with 1 master and 3 satellites. Haven't tried it but I'm curious what the satellite limit would be.

If you go back and review my previous post #93 above, that setup has been working for me for over two weeks now.  

NO TRAVELERS NEEDED AT ALL.  

Correct, it will NOT work with the 230.  Not sure what about the internal programming with the 230 won't let it work.  I tried.  No joy.

You can install a Kasa HS220 Dimmer or a Kasa 200 Single Pole switch at the location that actually controls the load.  Then, you can install a Kasa 210 anywhere else in the house you want, and using the app and the smart scenes I described in my post above, you can make ANY Kasa switch ANYWHERE (with just power, neutral, and ground connected) control the HS220 or 200 that you installed at the load.  Through the smart scene, the 210 just sends the command over the WiFi to tell the main switch (the 220 dimmer or 200 single pole) to turn on.  

As another user pointed out, there is a small time delay like 1 or 2 seconds between pushing the remote switch and the light actually coming on, but it works just fine.

My only complaint that I wish Kasa would fix is the status light on the switch.  The circle light on the paddle of the remote switches doesn't indicate the actual status of the light it's controlling.  I'm okay with that.

Ideal Solution:  Kasa should make it possible to tell the light on the paddle to reflect the condition of a remote load / smart scene.  (i.e. If my upstairs hallway lights are on, then the remote switch at the end of the hall by my son's bedroom should be off.  If my upstairs hallway lights are off, then the remote switch at the end of the hall by by son's bedroom should be ON so you can see where the switch is in the dark.)

Intermediate Fix:  I realize the ideal solution proposed above may be more complicated programming.  In the interim, and easier fix would be if Kasa would enable users in the Kasa app to just leave the paddle light on all the time (or off all the time if you so desire).  I would just tell it to leave the circle light on the paddle on all the time so that when the upstairs hallway lights are off, my son can find the light switch on the wall just outside his bedroom.  When the lights are on, it doesn't bother anybody that the cirlce light on the light switch paddle is on.

I plan to only replace the line-side 3-way switch with a smart 3-way switch, and leave the load-side 3-way and 4-way switches dumb.  However they both share gangs with other smart kasa switches, so I want them to match aesthetically. Does tp-link make dumb 3-way or 4-way switch replacements that match...at least somewhat?

  @ScottMan I am trying to install KS230's in a 4-way set up but haven't quite been able to figure this out.   Any additional help would be greatly appreciated.  I have a house full of Kasa switches that I installed myself so I have had plenty of experience with their products but this one has me stumped.  Here is more info on my configuration and for reference I am using the v2 version of the switches but it sound like you may have the original version.
 

My line and load are in the first box and so I used that as my master.  2nd switch is where the 4-way switch was located so I installed a satellite there.  Also a satellite at the 3rd switch.  My switch to switch wire is a 14/3+ground (black, white, red, copper).  At the master I am using red and white as travelers (red bottom, white top), black is connected to the load (coming back from the load out out on the satellite switches).  And then of course the master's line and neutral are connected as well.

Satellite #1 is the mid point so it has 2 reds on the bottom traveler connection and 2 whites on top traveler connection, black load is connected to the two black wires.

Satellite #2 is where I get confused.  Could you share some additional insight on what you connected to get this working?  In step 4 when you say load connected to traveler 2, do you mean to connect it to the load wire on the back of the switch.  Or connect to the black copper wire that is my load "loop"?  I am also confused on your comment about neutral passing to load.

Thanks for your expertise!

ScottMan wrote

1. line

2. master - connections out on travelers 1 and 2, as well as neutral

3. satellite 1 - travelers 1 and 2 connected to switch and output, neutral pass through

4. satellite 2 - takes travelers 1 and 2 with load connected to traveler 2, neutral passes to load

5. load

Note this is essentially replacing the 4-way with a satellite where the input/output travelers are connected together.

  @Indecision, my configuration was line coming into box #1 and load in box #3. Yours is line and load in box #1. This works, but you just have to bring the line back on the third wire like you are doing. So in the third box, you connect both traveler #2 and your load (black) wire to the traveler #2 screw. You won't have neutral in box #2 or #3, but you don't need it.

Hope this is clear!