The main issue is that it's a PvP zone. So i doubt it will ever happen.

First of all, Cyro maps have a queuing system. So you can't have a house that exits into Cyrodiil. Unless they make the Exit door take you to the Cyro queue, rather than loading you straight into the zone as normal houses do.

But the exit should also deposit you in your Alliance base probably, rather than exit somewhere into Cyro itself. Otherwise, the house would become a camping ground for gankers, killing any player that is loading into Cyro outside their door.

You would also have to disable the entry door, otherwise people could pop in and out of their house, when the only way out of Cyro is supposed to be the Wayshrines at the base camps.

So... if it's a Cyro house, but doesn't allow you to exit into Cyro, and you can't go inside it from Cyro only if you wayshrine to a different zone and then teleport to your house, and the exit deposits you at your Alliance camp rather than outside the house anyway, is it reaaally a Cyro house anymore? I think these are the issues that ZOS are facing.

They could of course make a Cyro keep house that has an entrance in a regular zone, but then it's just a house with a Cyrodiil skybox around it rather than an actual house in Cyro. But they could use those AvA keep models for sure!

They could make it something like a Legionnaires Suite where you have to have a certain alliance rank to buy it, and it is only purchasable with AP. It could be located inside a keep for each faction, which wouldn't break lore since it is to be expected that high ranking members of an alliance would get a nice room. It could be like 2 rooms and a cool balcony, and be styled for each alliance.
If you port to it from outside of Cyrodiil you just enter the queue for your main campaign, but it brings you to your suite instead of the normal spot inside the keep. From within Cyrodill they could make it so you could travel to it by walking in the door like a normal house or from the transit network, but to leave Cyrodiil you still need to go to the wayshrine.
IDK but a PVP house sounds super cool, maybe it could even have training room or something where you could have like 5v5 duels or something.

My neighbors above answered for the technical side.
I will answer from the point of view of lore:
1 - The house could be destroyed in a raid.
2 - Residents are expelled in a good part of the villages because of war.