I believe that the signals that Google will be using will continue to migrate massively.
A couple of primary changes which I believe to be on the horizon:
1) Things not strings
Matt Cutts has been talking about this for a while – the introduction of the knowledge graph means that rather than matching keywords to pages which feature those keywords, it becomes a move to meaning and actual language processing.
2) Natural language search
They intend to move Google (driven partially via Android and now Glass) to a full natural language model where we just say what we are looking for and this is translated into the meaning.
The outcome is a model similar to Star Trek computer eg just statements and questions.
3) Content
It has always been the ultimate driver but certainly after the last Panda / Penguin dramatics, most SEOs have hung up their SEO hat and focussed on the simple stuff that they can control.
I also am a big fan of usable tools to generate link bait and usage.
4) Social and usage signals
Google is sitting on a massive stockpile of usable user data and I am curious as to why this hasn’t been use more.
The main signals are things like bounce rate, repeated search rate (eg what was the last site found and then stopped searching), time on site etc.
Social I believe will remain a significant driver also.
5) Mobile impacts
Mobile friendly sites will be favored so continuing this focus.
6) Link building still important
I believe that this will remain important but it already seems more about ratios than volume eg
High PR vs Low
No follow vs follow
Etc
7) Authorship brand
This has been signalled for a while so the profile and social followed profile will become a part of this.
8) Bing and Yahoo still suck
Notice that I didn’t mention them. That’s cause I think that their quality is going to continue to stagnate in regards to Google.
Siri and Apple could actually become a part of the search eco system (eg leased by Bing?), but I do think that voice search would be big.
(This post was originally on Quora).