The benefit is already means-tested for those who are in receipt of Income-Based ESA. However the test is a simple one: ESA is payable if the applicant has savings of less than £16,000 and their partner (if any) doesn't work for 24, or more, hours per week (on average).
Income-based ESA is paid when the applicant doesn't meet the conditions for Contribution-Based ESA. That requires that the applicant has up to date National Insurance contributions.
Section 51 of the Welfare Reform Bill, currently before Parliament, proposes limiting the period on Contribution-Based ESA to 365 days:
http://www.publicatio...010-20120075_en_1.htm
The Bill has completed its passage through the Commons. The First Reading of the Bill in the Lords (which was simply a formality, introducing the Bill into the House) took place on the 16th June. No date has yet been set for the Second Reading.
Chris