Chrysalis hatches an evil plan to fillynap the new born princess, replace it with a changeling, and harness its power to rule Equestria!
...
Her children aren't as eager.

Author's (un)originality: I'm pretty sure there's ton of others who think this will happen in season six...but I wrote it anyway...ya know, just in case it doesn't.
ohmahgoshireallyhopeitdoes