First of all, masternodes will still be paid even if they don't serve lock requests. They're not being paid for performing the service. They are being paid and they perform the service, if they feel like it.
They are being paid for continuous uptime. Part of that uptime is locking txes. There is no reason to opt out of tx locking (or future services). What would that accomplish, saving a few CPU cycles?
I'll leave that to people who want to figure out how to exploit it. I'm not going to give them a free cookbook any more than I already have.
But I'd point out that even "a few CPU cycles" would be very significant if the system actually had real usage and adoption. TPTB makes good points on that.