Izzie and prom dress in the elevator was awesome, i would have been more touched if the door opened to reveal Denny, since it is their thing. And she has been having visions of him throughout the whole period while she was sick.
As for George, yes he did look cut and handsome in the army uniform, but he shouldn't have been in one, he technically didn't even go into the field yet!!! he should have been just the awesome old george that everyone saw and knew.
I would have been sobbing if it was izzie and george in the elevator being greeted by denny, because it wasn't already a surprise by the time izzie saw george, we all knew by that time that the john doe was george.
Symbolic, yes it was, symbolic an accurate terms, no it wasn't.
Izzie and George was always on the outs with the whole cast, so cliffhanger-wise i think izzie is just dead (she signed a DNR) and George if he was to come alive again, he's either end up with the amanda girl or continue his plan of joining the trauma team for the army.
I was also kind of disappointed how everyone is rushing to commit and love and get married all because of the whole izzie and alex scenario, not really from their hearts more from their fears.
like you, i was expecting denny when the elevator doors opened, but the shock of seeing george? or him in uniform?! completely knocked me back a few seconds, i couldn't register why he was there. i don't think the impact would've been that great if george AND izzie were in the elevator together, they walk out and denny's there. he's not that big of a significance to george, since, like he said, he's IZZIE's tumor, not george's hallucination. the scene wouldn't have been so great if george was in his scrubs =P i'm not too fond of rhimes. don't know why but she just.... gets on my nerves everytime i read her interviews.
i think at the moment, we can all safely assume george is out. he wanted out of his contract, and they ended his character with a definite ending (as opposed to Kutner just committing suicide out of the blue in House T_T) and regardless of izzie's DNR, you see bailey and the chief working to get her back. oh alex </3 everybody rushing to say their i love yous was a bit rushed so the only part i actually thought was cute was meredith & derek's marriage ceremony through blue post-its <3 buuuutt that's about it. not even seeing debra mooney made it a kicker for me.
Also, can anyone tell me how the elevator scene is so symbolic. I am having trouble connecting the dots. 
if you remember denny duquette then everything else is a breeze. it's the scene where the staff at SGH held a makeshift prom for one of the patients, which explains why she's in the prom dress get up. she gets in the elevator to get to denny's room. blah blah blah, he dies, the whole LVAD wire situation comes up, she's heartbroken, crying beside denny on the hospital bed and alex comes and picks her up to comfort her.
imo, i think it's just symbolic because in the previous season, she was going to go to denny in his room, so i'm going to believe that in this season as well, like before, she was going to see denny (and i'm going to attribute "seeing denny" as "seeing the white light" in ghost whisperer =P)