Kris

Call spreads go to zero, put spreads go to distance between strikes. Modal implied stock price at expiry : zero

Why?

The arbitrage upper bound of a call is the stock price itself. (A stock price itself is like a 0 strike call)

So all the calls go to the same price which means call spread is zero.

All puts go to their upper bound...the strike price. So all put spreads reduce to the distance between strikes. 

[Also if a 10 wide call spread is $7 then the put spread is worth $3. Algebraically, buying a call spread = selling the same strike put spread*]

*hand waving cost of carry and early exercise premium

Technically the call spread and put spread between of the same strikes sum up to the box spread. 

Box is a spread of synthetics 

+C, -P at K1
-C, +P at K2

Notice...that's just a call spread + a put spread

Fun stuff