Bitcoin cannot handle "spam transactions" properly and doesn't appear to have the ability to update to a blockchain protocol that would allow them to do so.  Unless I am mistaken and they have done so already?  Can someone cross check this please? 

Think of "sharded forks" not as a new chain but as a less trusted block.  Once a "shard" gains a certain amount of transaction volume, it should be verified by the unsharded chain.