Nope. There isn't any merging between Steam versions and currently existing accounts.

According to @ZOS_JordanH‌, in another thread: "No, if you were to purchase the game again through Steam, you would not be able to apply the key to your existing account."

TeraAngelos wrote: »

According to @ZOS_JordanH‌, in another thread: "No, if you were to purchase the game again through Steam, you would not be able to apply the key to your existing account."

Do have a link to his post please?

k9mouse wrote: »

TeraAngelos wrote: »

According to @ZOS_JordanH‌, in another thread: "No, if you were to purchase the game again through Steam, you would not be able to apply the key to your existing account."

Do have a link to his post please?

http://forums.elderscrollsonline.com/discussion/120432/adding-eso-to-steam-library

TeraAngelos wrote: »

k9mouse wrote: »

TeraAngelos wrote: »

According to @ZOS_JordanH‌, in another thread: "No, if you were to purchase the game again through Steam, you would not be able to apply the key to your existing account."

Do have a link to his post please?

Unfortunately, I don't, as his original post was quoted into another thread. The thread it was quoted into is here: http://forums.elderscrollsonline.com/discussion/120431/any-way-for-existing-customers-to-get-the-whiterun-wolfhound/p3, posted partway down by @IcyDeadPeople‌ (he may be able to shed more light on the specifics). I am trusting it has not been taken out of context, though I may be wrong.

Edit: Thanks to @Xiana for providing this information

If I understand correctly, if we purchase a new copy of the game on Steam, we will not be able to link our old account to the new one, and we will not be able to log in to our old account through the Steam library.

ZOS_JordanH wrote: »

@IcyDeadPeople‌ No worries. Always happy to provide clarification!:

...however, does this mean if I were to purchase a second copy on Steam, I would not be able to use the Steam library to open the ESO launcher and log on to my existing account?

Purchased Steam versions of ESO show up in your Steam library. When you click "Play" within Steam, it will open the regular ESO launcher to start the game. A new copy of the game purchased through Steam cannot be linked to a pre-existing ESO account.

As stated earlier in the thread, you can add your current version of ESO (attached to your current account) to your Steam library as a Non-Steam Game. When you click "Play" within Steam, the ESO launcher will then open, just as above.

Or would it be possible to purchase a new copy on Steam, add it to our Steam library and log in with our existing ESO account, just keeping in mind we don't get the 30 days free game time or vanity pets, etc?

Again, if you were to purchase a new copy of the game through Steam, you would not be able to use a pre-existing account with that copy. You would need to create a new, separate ESO account.

We hope this clears up some of the confusion!

The friend's house idea / story

If I go to a friend's house and try to log in with my account via their computer, I should be about to see everything that I own on that account.

Having Steam on ESO is like going to see the friend's house, I should be able to log in with my current account (I do not get any 30 days free, pets,etc those are for new accounts only)

https://help.elderscrollsonline.com/app/answers/detail/a_id/21646/kw/Steam

HOW DO I PLAY ON ESO FROM STEAM?
Updated 07/17/2014 02:26 PM Published 06/26/2014 09:32 AM
Players who purchased The Elder Scrolls Online on Steam will of course be able to launch the game from the Steam Client. To do so, players need to install the game:

In the game Library on Steam, select The Elder Scrolls Online and click Install.
Once the installation begins, click on Finish to close the installation window. Players can track the progress of their installation in the Steam Downloads view.
When the Installation Options window appears, players can indicate whether they wish to create a desktop icon, choose a megaserver, and select the language in which they wish to play.
Once all preferred settings have been selected, click on Install in the lower right corner of the window.
Near the end of the installation process, an in-launcher window will prompt players to activate their ESO accounts and select a subscription plan if they have not already done so. They will have the option of selecting either Activate My Account or I Already Activated.
Players who select Activate My Account will be redirected to The Elder Scrolls Online Store. From there they will need to create an account, redeem the code provided by Steam, select a subscription, and register their payment method.
More information about subscription set-up can be found in this article.
Once players have an active subscription plan and the game installation is complete, they can press Play on the game launcher and begin their adventure.

Now I am confused!

What happens if I select " I Already Activated.?"