No Slim Arcade. Sell the Slim Pro's and Elites for the same price/or cheaper as the current models. Just like a Sony slim PS3, if players wanted it they would have to buy it and sell their current PS3 (or keep it) the same can be done for the 360.
You wont NEED to update to a 360 slim, if you do you will have a harddrive come with it so you don't need to worry about that. They could bundle one of those harddrive transfer kits.
As for taking your 360 slim harddrive round to a friends house (and vice verser) they could bundle (with all consoles) a connection kit for the two, in the form of a cable or something else, won't look pretty but it solves the problem and you are only taking it over to play games on your friends 360.











