Can someone explain to me what the rationale is for only providing enough CAIx to exchange about 80% of the supply of CAI that was mined? 

I have been mining this along with a number of other currencies and don't have the free time to read every thread post for every coin in its entirety.  I was relying largely on updates to the website and OP for information on exchanging CAI for CAIx.  I think that if there was going to be a hard deadline on making one-to-one exchanges, it should have been in the OP and in bigger, bolder lettering than the nearly meaningless updates.  Scanning through the posts, I would see a lot of discussion about CAI mining ending, but relatively little mention of the game of musical chairs that we were apparently playing.

In the end, I only spent a few dollars worth of electricity to get CAI that were worth something like $25 last time I checked--so this isn't the end of the world.  But I think it's worth mentioning that this doesn't seem to have been handled very well (unless I'm missing something, which I very well might be).