Are we sure that Matt is doing Salsa tonight? Source? I would have thought it would be ballroom tonight (ie so they are not exhausted for the swingathon) - ie 2 VWs, 1 QS, 1 Tango and 1 AT.
And for Soulmate - the Swingathon will basically be a mixture between Rock n Roll, Jive, Jitterbug, some Hustle (maybe) based on West Coast Swing or East Coast Swing ... - basically it will be a bit of everything.
One of the main steps in West Coast Swing is call the Sugar Push (cross between Jive basic and a CCC figure (coming together then separating). The first half of this step usually preceeds any number of figures including lifts, swings around shoulders, back and forward through the legs (something Brian and Kristina did a lot), the round the world (when the woman is swung round the back of the man and she swings round whilst he is only holding her legs... [sorry not a very good description].
It will be exhausting for the ones that reach the end.
Bearing in mind that all the couples will dance at least 40-50** seconds together before anyone is eliminated (or it wouldnt be fair to elminate anyone before this time to give them a chance), and say they eliminate another couple every 20-30** seconds later, the last two couples are likely to be dancing (at a minimum) double the time they usually spend on the dance floor.
Only the ones with the most stamina will last. [I know I have tried to do a similar thing at a CCC competition which is not half so draining u usually have a round routine of usually a minute that you repeat 2 or 3 times - but by the time you get to the 2nd/3rd time round it gets hard to keep posture and discipline yourself to do the routine as cleanly then unless you have boundless stamina.]
[** and these estimates could well be much longer.]