There's a limit on the price not least because too much electricity would be used to mine the coins.

i.e. If BTC were to go to $500,000 in this era it would cause a catastrophic mining bubble:

   $500,000 x 25 = $12,500,000 per block = $75,000,000 per hour

   $75 million per hour would drive the mining to attempt to use 675 GW.  This is about 30% of all the power generated on the planet.

Ref: https://bitcointalk.org/index.php?topic=518111.msg8674306#msg8674306