I'm afraid Richard Seymour has it plainly wrong here.
First of all, he clearly overstates the strategic coherence of Syriza by stressing a Gramscian-Poulantzian "reading" of the line followed since four or five years. Of course there are people within Syriza, including myself, who try to intervene along those references -although certainly not in the sense of a supposedly 'cross-class' project of social and political alliances. But the line effectively followed by the leadership is overall characterized by tacticism and pragmatic adaptation to a shifting conjuncture. With one exception: the Spring 2012 proposal of a "leftwing anti-austerity government", which is now partially - but only partially - realized, and with a level of distortion.
Secondly, it is true that Syriza has softened up its position on the issue of the banks, but not only the banks. The softening also consisted in emphasizing the perspective of commonly agreed solutions ("win-win deals") on the issue of the debt, dropping the demand for a citizen's audit of it and avoid any talk on default. But even that line remained unstable. Most importantly perhaps, Syriza's style adapted to a situation of decline of social mobilization and put forward a more "parliamentarian" type of political intervention (without however breaking with grassroot work or cutting links with the movements). I gave some more detailed explanations on this in my Jacobin Magazine interview. But what needs to be stressed here is that the "softtening of the line" has not been a trade-off between a "harder" anti-Troika "national" line and an attenuated "class" dimension. It actually meant a (partial) retreat on BOTH fronts.
Thirdly, when Richard writes "this strategic idea of, to give it the 1970s Gramscian gloss, a 'national-popular', cross-class alliance to break the memorandum, has a very definite referent in the nature of the Greek struggle and in Syriza's analysis of Greek capitalism" I think he's entirely mistaken. No one has ever defended this type of line in Syriza, it is completely alien to all the variegated political subcultures of the party. In the Greek context this approach is typical Pasok 1970s "populist developmentism", of the Samir Amin, André Gunder-Frank version of the "centre-periphery" theory, and, historically speaking ALL currents of Syriza, whether Eurocommunists, Trotskyists, Movementists, or more traditional Communists have constituted themselves against it (with the possible exception of the Maoists). The rightist elements in Syriza, more particularly the two leading economists, defend a very mild form of Keynesian recipes softened up to look (on paper at least) compatible with the EU treatises. And the remaining few right-Eurocommunists (of the Platform 2010 pro-DIMAR tendency) just advocate a soft adaptation to globalization via the European integration channel. So even in that direction there is nothing remotely resembling the type of thinking Richard is referring to in order to provide some kind of "strategic" background to the alliance with ANEL.
This alliance has been, I'm afraid, a forced and quite pragmatic type of choice, devoided of any grand strategic design. And since Syriza's offer of an alliance with the other force of the radical left has been categorically rejected by the latter, this possibility has been explored since a while and was therefore easy to materialize once the election result was known.
But more on the ANEL in a forthcoming post.
I will obviously defer to Stathis on all points concerning the concrete cultural and ideological defaults of the various groups and subcultures in Syriza. The only point I would insist on is the methodological one, viz. that the 'pragmatic', technicist adaptations of the Syriza leadership implies a theoretical substrate and a strategic logic, whether one gives this a Poulantzian-Gramscian gloss or something else. I'm not so much concerned here with what Syriza's leadership 'thinks' it is doing so much as with the (perhaps subterranean) logic of what it does. So that even if my answer is unsatisfactory, to say that Syriza's decision is devoid of 'grand strategic design' seems to sidestep this problem.