@Tanquen I got the new Nest one the other day and it works well. The wired backhaul is automatic. I set up the mesh with 2 of them and unplugged the main one from power and the second one just kept the Wi-Fi Internet connection going. Nice. :)

Great to see so many replies to this - shame more of them were not from TP-Link offering to upgrade.

I have a question for anyone who might know the answer. On the basis that we are unlikely to see wired backhaul on the RE700's then I may splash out on a set of thee Deco units (AX1800).Question is - could I use my AX5400 to "host" the onemesh system and control the three new AX1800 devices via Ethernet plus perhaps the three RE700's on wireless (need to be within range of the main router). This would give me a onemesh system with a main router and 6 satellite devices (three wired and three wireless) and would be sufficient to cover our (fairly large) house.

  @JP_NL 

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Ethernet backhaul for ALL meshOne devices is mandatory!

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  @YH1 If you have the newer faster Wi-Fi mesh routers with three or more channels, it's not as big a deal as it can use one of the channels for direct communication between the other nodes. But with the ethernet port already there, it seems silly to not offer wired connectivity.

  @Tanquen

I agree that wifi can solve some of the cases.

However, when there are obstacles in the way, the wifi signal is significantly affected and causes poor signal and speed or no signal at all. 
That is the reason to wire your house in the first place. :)
Btw, in 6E routers, if that is what you meant in the newer router (that has not arrived in my region yet)

The 6ghz is even worse than 5ghz in penetrating walls, I have a 40cm concrete wall. 
I have the AX11000, 8 ethernet ports router, and not having the Ethernet backhaul in that kind of router makes me think that tp-link product engineers don't really understand the use case of 8 port routers... :)

  @JP_NL 

Clearly those people who design these things live in paper houses where a wifi signal can get everywhere. For those in the real world we need Ethernet. I have at least two course of brick between each room and pretty much have an access point in every room. The concept that all of these can reach the main router via wifi is for the fairies.