There was a CATO Institute forum on C-Span last year and one of the guests was from the Bush administration. She said the worker program would be open to every sector of the economy and that if they had kids they would automatically be citizens. The plan was and still is to force all Americans to compete with foreigners for jobs in their own country.
Btw I agree with you, if the guest worker program were limited to only agriculture then it might be far more easier to swallow.
Can you imagine the level of animosity towards these foreign workers if that happens?