Bitcoin blockchain size practicality
Work is being done on cleaning up the database by getting rid of obsolete data, although full nodes would probably always want to keep everything. 

Also note that non-full nodes, like a wallet app on your phone, don't need the full 19GB at all and are really quick already.

Also keep in mind that disk size and network speed keep growing as well, so we still have quite some time to go before this would really become a problem.