Nobody is talking about forcing the blockchain to expand at pre-set dates. Nobody is talking about forcing the blockchain to expand at all.  The block size increases automatically with demand, as it always has.  The blockchain doesn't automatically fill whatever the current cap is.  The cap has been 1MB for years now, and we don't have 1MB blocks yet.  

Whether we do nothing, or whether we adopt BIP 100, BIP 101, etc, the block size will continue to slowly grow naturally as adoption increases.  With no change to the cap, that growth will be stopped in its tracks in about a year.  The 1 MB cap was added as a temporary solution to the worry of a spam transaction attack, which hasn't yet materialized.  To maintain the 1MB cap and artificially restrict the relaying of valid transactions would be a radical departure from what Bitcoin is.