The yellow triangle represents the sort of "Zone of Compromise". I'm pretty sure that a co-ops provision, with immediate implementation, could pass the Senate (or at least not be filibustered by it). Likewise with Olympia Snowe's trigger. A strong-ish opt-in amendment proposed by Maria Cantwell was approved by the Senate Finance Committee along party lines, but did not get Snowe's vote; it might or might not pass the full Senate.
Basically, any square that is overlapped by the triangle seems like a plausible outcome. The most robust public option available is probably a federally-run program that states would have the right to opt out of and which would have to negotiate its rates in the market. The worst-case scenario is probably state level programs with an extremely stingy trigger, as proposed by Snowe. (This is assuming, of course, that health care reform as a whole will pass, which people may be a little bit too sanguine about.)
This is not a perfect representation of the alternatives by any means. Co-ops and government-run programs are not necessarily mutually exclusive. A "loose" trigger could conceivably be more robust than an opt-in provision, or even an opt-out provision, although in practice Snowe's proposal is not. Moreover, state-level options and triggers could be combined in various ways: maybe states have to opt in initially, but they'd be enrolled automatically if a trigger kicks in. An final complication is is that certain of the options -- for instance, a state-run opt-out -- do not make particularly much sense. Still, it should provide a reasonably useful schematic.
from 538, the link in the OP.
http://www.fivethirtyeight.com/2009/10/public-option-playing-field-in-two.html