I'm just going to show some of the research I've been doing today on the glyph in the teaser, and let you decide if it's related to Spellcrafting or not.

Let's start with the teaser picture, specifically the one with the tablet pushed close together to see the glyph better:



(And here's the full teaser image if you haven't seen it yet - ClassyKatie, a popular ESO Twitch streamer, got this in the mail a couple days ago from ZOS. ZOS has since retweeted it, so it's official)
Indeed, my first thought was Spellcrafting, simply because I couldn't think of anything else, but just that alone didn't satisfy me, and I didn't want to get my hopes up like that so easily, so I checked a lot of symbols that it could be: Mage's guild, Psijjic, Elder Scrolls, etc. and nothing came up.

Then @ZunaRoath found that in an addon called Essential Housing Tools there is a feature called "FX" that lets you put up various effects in the house, some of them seem to be added by the author, but others seem to be drawn from the game files, and of those, one of them is completely identical to the glyph shown on the teaser tablet. I then used the addon myself, and here's a screenshot I took, rotated so that it matches the direction of the glyph on the tablet in the teaser.



I can't seem to find that glyph anywhere else on the internet, but apparently it must have been in the gamefiles for awhile. It's listed as "Sigil, tablet" in the addon. A bit strange, actually, since there are no tablets in-game with that glyph on it, just the tablet in the teaser. Were the devs planning long beforehand to have the glyph tablet be a teaser, long enough that they had the glyph in the game files reference that tablet? Possibly, but there's another explanation, but I'll get into that later.

So, the glyph matches the one in the teaser. That doesn't mean it's Spellcrafting in any capacity alone, of course. I looked at some of the icons for the Spellcrafting glyphs shown back in 2014 and at first was disappointed with my findings, until I went and actually watched through the video where they show the tablets with the spells and the like. Here, I'll link the video, it's an interesting watch!

The Spellcrafting segment starts at about 53 minutes in: https://youtube.com/watch?v=_Jk7LrLgRfg

If you watched the video, you'll know that the glyphs for each spell is different. Here are some various spell glyphs shown in the video:







You'll notice that none of them match the glyph on the teaser tablet - but, since we know that the glyphs for each spell are different, perhaps the one on the teaser tablet is simply just a different spell than the ones shown in the quakecon video? The real question now is - do you think the glyph on the teaser tablet matches the "style" of the spellcrafting glyphs. I'm not quite certain, there seems to be a lot less circular designs in the glyphs, except for the first one, which is different for other reasons, and our teaser glyph doesn't have any script!

However, if you look at the second glyph - the flame atronach one, and look to the top right, you'll see a blank version of the glyph that looks a bit eroded. Perhaps then our teaser glyph just isn't complete, then?

Two last final pictures for you, and these are the ones that made me decide to make this thread. The doorway to the spell glyph room in the quakecon video.



And a version of it that can be found in the FX feature on that addon to get a better look:




Now, I don't know about you, but I would say that the door glyph definitely matches the style of the glyph on the teaser tablet. It's just missing the writing. It's not a perfect fit (but I did try putting the two over each other, and the writing of the door glyph, and the dividers, actually do line up pretty well with the teaser tablet glyph, but not the circle placement)

So, because of that, I'm starting to consider the possibility of Spellcrafting coming soon. I was a bit hesitant to come to this conclusion, due to the likelihood that it was scrapped once again for balancing issues, and especially because of an anonymous claim from a class representative who has spoken to Rob Garret a few months ago, who claimed to have heard from him that it was indeed scrapped again. Here's the screenshot:




And yet, despite even that screenshot, seemingly insurmountible evidence that denies the possibility - I just can't seem to come to any other conclusion that has as much evidence to back it up, and consider this: they want us to speculate and "put the pieces together", right? So why would it be something that means absolutely nothing to us until the full reveal - if it's not something we can piece together. Spellcrafting is, because we have old information on it to compare to. I can't think of anything else that we could even begin to work out what it could mean otherwise. Maybe you can?

Oh, and that bit about the "Sigil, tablet" possibly referencing spellcrafting just from the name. Tablets are said to be quite involved in Spellcrafting from the quakecon videos. Tablets are where you find the spells, and what you use to recreate them, so the word tablet is pretty rooted in relevance to Spellcrafting just by itself.

Anyway, that's all I got. If it's not enough to convince you, then I hope it was at least an entertaining read!