Much of the time secession is the goal, sometimes it is just a pathway to union with a homeland. Yesterday, Crimea could be either. Today? Looking more and more like irredentism. Lots of separatist movements end up dividing over their end goals with the various Kashmiri groups being the best examples, but since Crimea's separatist movement seems more of a creature of Moscow than a genuine secessionist movement, that kind of debate of where to go is not happening.
To be clear, irredentism can be and often is inconsistent, so what Bill and I wrote for the Monkey Cage yesterday still stands. I do not think that Russia is aiming to unify all or even many of the lost Russians and their territories in a Greater Russia. Putin's own statements are contradictory, so his nationalist appeals are actually quite muddled. Also, Crimea is one thing, but Eastern Ukraine? That would not be a fait accompli and would most likely require war.
Of course, geography here raises some questions--how can Russia support Crimea if it does not have any land between Russia and Crimea? Sure, Alaska is not exactly adjacent to the rest of the US, but Alaska has its own fresh water and can produce its own power. Crimea? Apparently not so much. They could build a bridge to tie Russia proper to Crimea, but that will just help facilitate the flow of subsidies that will cost Russia a decent amount over the long run (irredentism is rarely profitable in the sense of making money--it tends to be costly, which does not necessarily deter it).
This also represents a shift for Russia from supporting quasi-independent frozen places--Transnistria, South Ossetia, Abkhazia--to actually annexing hunks of former Soviet territory. So, there is much room for concern.
But all of this seems like quite ad hoc. There is no master plan for grand reunification since Putin would have been pretty happy a few weeks ago with his man in power in Ukraine, and Ukraine remaining independent but highly influenced by Russia. With that no longer in play, then it seemed like Crimea could be used as leverage, but now it is spinning a bit beyond that.
Do we really know what is going on? Probably not, as I don't think Putin does. Still, there are plenty of insights over at Monkey Case, Duck of Minerva, and other places. This is not the first time we have seem various aspects of this crisis, so our understanding of these past events can be helpful here. Still, ours is a probabilistic science at best, and we tend to gloss over the role of individuals. In this case, the perceptions, reactions, and predilections of an individual, Putin, matter a great deal.