Agreed, Tau are little more then children in the eyes of the Eldar, however, even they noticed their progress and the develpment of their tech. But since they cant use or sense the warp/psychic stuff they are at a disadvantege with supply lines, interstellar travel, ect.
And yes, Eldar can appear out of nowhere without notice and slaughter anybody silently and efficiently.
Also their psykers are the best there is, technically no competition (only maybe Ahriman and their ilk).

However I do like both of their lore, storyline, charactersm doctrine and combat style ^^ but yea they differ a lot but similar in some ways. Hence why the Eldar consider the Tau worthy of some thought.

Don't forget Librarian Tigurius, he achieved to enter a Hive Mind and leave it again without going crazy.

But besides that, the Tau are very strong and they NEVER make a mistake twice, that is what makes them so dangerous. Once a Tau was tricked he won't fall for the same trick a second time. Against Space Marines and Chaos and obviously Orks that on the other hand can work. The Tau are adaptive in tactics as adaptive the Tyranids are in evolving.

Nonetheless I personally think the Eldar are very aware of the Tau's danger towards them but do not really care about them just yet and rather see in them a potential ally to defend the galaxy against Tyranids and Necron, since they are praising "The Greater Good" it would be easy to convince the Tau to forge a temporary alliance to defeat a Greater Danger, just as the Devourer, Necrons or Warp Daemons.

There is a speculation that Tau are artificial species made by Eldar to eventually replace humanity, which proved themselves weak and prone to corruptions of different kinds. Look at the Lexicanum for said speculation.

Appearance of the first Ethereal right in the time where Tau were about to destroy themselves in ongoing brutal civil war, and "sudden" warpstorm, striking an Imperial purging fleet, support those speculation.

But there is no possible way non-psychic Tau can get an access to a Warp. Or even guess that there is a Webway without someone telling them. So, they hardly pose a threat to their supposed creators at all.

I doubt it personally, though Tau and Humans share a lot... Both are Imperiums. Both have a system to classify their objectives. (E.G. Adeptus Terra / Administratum and the Tau having their different Castes or however it is called in english ; only know german terms, sorry)

Not to forget "The Greater Good" can be very equivalent in use of Termology to the use of the "God Emperor". Also since the Tau are apparently not available to really use the Warp and have not many Psyker's it would make them immune to the Chaos gods.

And their tactics, in my opinion they always seemed to be a hybrid of Eldar and Space Marine tactics. Swift and devastating like the Eldar, but also with a lot of raw firepower if required like the Space Marines.

So perhaps they could be seen as a race made by Eldar hand, but as I say I doubt it.

Well, some Rangers of Alaitoc stole some space bug queen with no apparent reasons. Said queen had pheromones not unlike Ethreal ones. That speculation goes from where and some misterious points in Tau history add weight to it.

But, sure, i'll be kept in that way without actual solving. That's always had been the part of the 40k lore - there are different point of views, but the truth is hidden.

It's possible that Tau are naturally evolved species which at some point of history received some "help" from Eldar who had seen the potential in them (hey, seeing the future is our thing!). Well, they didn't make a mistake.

Anybody got a feel of bit of a similariy in the story of the Tau and the Protoss ?
They both got a highly evolved/tech race to help them out

Oh you mean the Protoss from Starcraft from the company that stole as good as everything from Wh40k to make starcraft? I only love to say at this point whenever Starcraft is brought up: Hydralisk vs. Ravener

Anyway I love Starcraft, the games got good stories but I will never forgive them for stealing the wh40k stuff.... At least better than what C&C Alliance (the F2P game) did to Wh40k with stealing vehicles 1:1 from the Orks lol!

Did you know that originally Starcraft was not Starcraft but an GW ip game ? With Nids, SM and Eldar :3
They removed themselves half way from the production, hence the marines armor why looks so similar to SM power armor, Zerg --> Nids :3 Ect ^^
I smile a lot when ppl say that WH40k stole from SC But lets leave it at that, since I dont want a needless SC vs. WH40k debate here :3

I guess the Eldar are the most 'alien' race, this is what I think makes then attractive to play. They look like you, at first you think then are the closest race to Humans, you think you start understanding them... and they show themselves to be as merciless as Tyranids, savage as Orks, patient and 'computer minded' as the Necron, stuborn as the Humans, crazy as Chaos... Finally, you understand that they are so far from what you first believed, and that you will never understand them.

I think the possibilities they offer are infinite! The fact than you can create your own Craftworld for fun with every caracteristic you like is a lot of fun too. Finally, you can create all kind of silly names with hidden jokes or double-sense quotes when naming then! ;-)

Si proches, mais pourtant si éloignés...

Dont mind this, had to snatch the 100th post in a thread I thought would have died awhile ago, you eldrich chaps are pretty nice.