There remains the option of growing the block size automatically if more than X % of transactions take longer than Y hours to complete. This will ensure that a healthy fee market will still exist despite Bitcoin's unlimited potential growth. I also believe that Bitcoin will self-limit if "too large" blocks sizes poses any security issues - due to the amount of FUD that will be created...
However this is unlikely to happen as data speed and memory/storage cost will keep improving which means Bitcoin can grow at least at that rate without any loss of decentralization or orphan block concerns. I subscribe to Ray Kurzweil's interpretation of Moore's law (cost vs processing power) as it is the only one that matters for the purpose of any discussion around Bitcoin: http://www.danielcelton.com/2015/10/19/moores-law/.
Is there anything wrong with this argument?