The "forced transaction fee is simply an anti-spam measure. As block rewards decline miners (or more specifically) will start to decide that transactions they will include. For example pool xyz could announce they won't include any free transactions. If other pools follow suit then transaction fees will increase. There is a problem in that the network/protocol allows 1 satoshi transaction fees. Most likely no pool will reject a paying transaction and there is no reason for sender to pay more that will keep transaction fees unsustainably low.
The good news is we have plenty of time to establish a functional "fee economy" as hashing power (and thus difficulty) is likely 2x to 3x higher than it needs to be relative to the economic value it protects. Bitcoin right now is like a private army with 10,000 troops, state of the art equipment, gunships and tanks to protect a baseball card collection.
Do you have any thoughts on how this will affect gpu miners who actually have to pay for electricity?
Fpga miners will naturally continue mining i guess.
As a gpu miner who does Not pay for elect i am mining just as long as it is worth my time. For example i just RMAd a card
Which cost me 15 dollars for a processing fee as well as shipping, crappy sapphire 5830 company, and if this happens more as time goes on with shrinking profits i will say it is time to quit. Now add in costs for elect, if i was paying it, and i could see many people quitting.
And as the other person mentioned i do pay attention to diff.... But if one waits too long older radeon cards loose their value.
Eventually one needs to decide...