
Not really a surprise.
It's the only way to make up for the limited house themes available (as of yet), and to ensure players in cross faction guilds aren't cut off from customization options. (Aside from the nighborhood in on itself)
Trolls are part of the horde too, and trolls should be known to the Arathi, given the whole Humans and High Elves joining hands to defeat the forest trolls, likely being a origin story for them. So, you have undead, and two types of trolls (three/four with Haranir/amani).
We also have absolutly no idea what other races the Arathi might know of. Another tauren tribe? other titanforged races? eredar from the legion invasion?

Okay, so you might be able to have a Nelf house in a Horde Neighborhood

It was mentioned in the very first rundown of the expansion on the site. No detail about what Simplify would mean though.
https://www.mmo-champion.com/content...r-and-Features
Honestly, I don't see the issue with being able to freely choose what kind of hosue you want. Just like transmog, the benefits far outweigh the potential scenario of everyone looking terrible. Mostly because players generally don't choose to run around in terrible mogs, or in the case of houses, intentionally troll by making it look terrible.
The world revamp dream will never die!
I strongly disagree that faction by themselves are the heart of the game as we've seen plenty of MMOs with that same faction feature (Warhammer, Aion, Wildstar) and they all failed compared to Warcraft. Also, it's funny enough that one of the things that made people come back to the game was actually the end of most factions' limitations back in DF (also the expansion just brought a lot of new systems so it was a good gameplay experience despite the average lore).
I do agree tho that the cultural identity of each race was a major element in term of lore. And while I now despise those limitations, I'd say that the fact some classes were restricted to some races helped a lot of people to play a tauren, an orc or a dwarf instead of a human (and later an elf). And the game should keep focusing on those lore elements instead of pushing the same human / elf heroes over and over.
Most people stopped following the lore when the orcs became soft, when the trolls became civilized and when the undead stopped in their attempts of reducing all living creatures into undead nightmares.
I'd say that the current concept of factions is outdated. Players should be free to move wherever they want. The game should stop focusing on big factions and go back where it really shined, with small groups fighting each other. That's an exemple I like to give, but in Vanilla you don't really have faction lore of faction war :
-Just in Stormwind, you've got Goldshire's troups who struggles against gnolls, murlocs, kobolds and defias.
-In Westfall, you've got the People's Militia who fights against the Defias threat.
-Redridge is once again Stormwind's army vs the Blackrock.
-Duskwood is Night Watch vs undeads and worgens.
-Last but not least, Stranglethorn is Kurzen's deserters vs Kurzen's troups, trolls and the local wildlife.
That's something we've had in BFA and somehow in Shadowlands (but Shadowlands' covenants felt so out of lore that it was hard to even care about them) with Kul Tiras' waterspeakers, inquisitors, pirates or army.
Everything about actually creating the house is unbelievably great, but the design ramifications of neighborhoods keeps creating friction for me. And makes the barriers to private neighborhoods even more grating. The worst part is that, in the end, there's almost no chance neighborhoods will achieve their primary goal of fostering community.
Hoping we get Draenie exteriors.
Not a huge fan of the race but always loved their alien futuristic naaru architecture.
Gonna go for a techy alien vibe with Draenie, gnome and ethereal interior stuff as much as I can to trigger the high fantasy purists.