Reply #14: Texas already has a program like this. There are income limits.

[Liberal In Texas]

INCOME LEVELS

These are the maximum incomes for people eligible for the program:
Size of household / Maximum annual net income

1 $32,490
2 $43,710
3 $54,930
4 $66,150
5 $77,370
6 $88,590
7 $99,810
8 $111,030
Over 8
Add $11,220 for
each additional member

VEHICLE CONDITIONS

Your vehicle must meet these conditions:

• Failed an emissions test,
• Registered in your participating county area for at least 12 months preceding application, and
• Passed a Texas motor-vehicle safety and emissions inspection within 15 months of your application and driven under its own power to the automobile dealership.
-OR-
• At least 10 years old and gasoline powered,
• Driven under its own power to the automobile dealership,
• Registered in your participating county area for at least 12 months preceding application, and
• Passed a DPS motor-vehicle safety inspection (if more than 24 years old) or safety and emissions inspection (if 24 years old or less) within 15 months of application.

• $3,000 for a car, current model year or up to three model years old
• $3,000 for a truck, current model year or up to two model years old
• $3,500 for hybrid vehicle, current or previous model year

As you can see, you can't just go out and but a junker and trade it in for a rebate.
Also, the income levels make it less likely that a qualifying family could even afford to buy a new car.
So, if you need a new car would it really be worth the wait to see if and when a bill is passed that you might qualify?

http://www.tceq.state.tx.us/implementation/air/mobilesource/vim/driveclean.html