First, let me start by quoting Obama's official website: http://www.change.gov/agenda/urbanpolicy_agenda/
Scroll down to Crime & Law Enforcement, and read the very last statement. It's quite clear as day:
They also support making the expired federal Assault Weapons Ban permanent.
That being said, here are my thoughts to your questions:
-With everyone scrambling around to buy what they believe may soon be banned, how likely is it that the government will gain the power to seize these weapons or make them, ammo, licensing so prohibitively expensive no one can afford them?
Seizure of existing weapons, I believe is an extremely unlikely scenario. That would require excessive force and turn this country into a totalitarian police state, if not push us to the bring of civil war, as many would fight back from government overextending itself.
Now, as for taxing firearms, ammunition, and/or requiring crazy licensing, that is a much more probable method of "gun control" that could be enacted. I don't have exact references at hand, but I had read that Obama and Biden had stated that they wish to increase prices upwards to 500%.
-Will handguns be affected and to what extent? I assume the high capacity mags again but what about threaded barrels and rails? I've been itching for a 45 and assumed they would be unaffected.
There is no good reason to presume that handguns would not be affected, as they were also covered in the previous assault weapon ban of 1994. Recall that Biden was a champion of that ban, and Obama hails from Chicago, where King Daley believes that all handguns are instruments of Satan.
-Is there even a glimmer of hope that the Supreme Court ruling on legal handgun ownership in DC will make its way to Chicago?
The Supreme Court's ruling, while it sort of helped our cause, also skirted the issue. Others can explain it far better than I, but in a very brief nutshell, they said that outright bans are illegal but states can still regulate firearms ownerships to reasonable extents. What reasonable means however, can and will still be fought over.