Suppose that, for a married couple, both are on an independent H1-B visa with one of their I-140 approved. Suppose now that it is the end of 6 years for both. By virtue of the I-140, one spouse can get his/her H1B renewed. The other might have to go on to the H4 visa. Given the recent change that H4 spouses can work, is there are 6-year limit there too? Does that fact that the spouse has already used up 6 years prevent him/her from getting the H4 work ability?
The H4 spouse can apply for EAD. This situation (both spouses working, only one eligible for future extensions while pursuing a green card application that would benefit both) is exactly the issue the H4 EAD was meant to address.
The H4 EAD is not an extension of H-1B status, it is general permission to work. There is no tie to a particular employer and one's prior H-1B history isn't relevant.