the van flashed because it had Sayid's blood in it.
Blood Magic is even stronger than Ash Magic.
Remember the Zodiac and the clothes everyone was wearing flashed all over time.
the rope Sawyer was holding at the well flashed.
anything with blood, sweat and/or tears on it flashes ... anything with the DNA of the Chosen flashes.
on the subject of DNA : DNA performs a function of duplication, using RNA as the key.
Genetically it is possible for duplicate bodies to be created and magically it is possible to divide the soul if you have murdered someone [according to Harry Potter books]
Jack and friends have that in common ... they have all murdered people, though some have attempted to justify it ... Jack has killed people who shot at him .... it is murder to kill 3 or 4 people randomly just because they shoot at you ...
long story short, Jack and friends fit all criteria for having their bodies duplicated into another time-stream and have a part of their soul placed in those other bodies for a purpose ... when they have learned their lessons, the alternate reality will cease to be, for they will reintegrate into their whole selves .... if you listen to what the creators of the show have said about the time stream integration before the end of the show, in this light, you can see how this is possible.
remember how Charlie said to Hurley off island that he was dead but he was there. is this the Charlie that we see not dying but landing in LAX?