I was an H-1B worker myself and was following this rule making progress. The rule was not something new -- it was lobbied by big name software companies, and has been on DHS/USCIS's policy making agenda since 2011 at least:
The rule, as its currently proposed form, does not provide automatic work authorization to spouses of all H-1B workers. Rather, it allows "certain" H-4 spouses to be employment authorized. The subset of eligible H-4 spouses are defined as those "who have begun the process of seeking lawful permanent resident status through employment" and apparently before finishing it. Specifically, their H-1B spouses had to be in H-1B status for more than 6 years and are the beneficiaries of certain pending or approved employment-based immigrant petitions or labor certification applications.
Congress employs numeric control over the number of employment-based green cards that can be issued each year. The process is very complicated, and the wait time is highly dependent on the country in which a beneficiary was born and the category of green card he/she sought. For beneficiaries from most countries, the wait for an employment-based green card (once you had an approved petition) is far less than 6 years. The only country that currently suffers a more-than-6-year backlog is India, whose current line for the "EB2" category is 10 years, and "EB3" 11 years. The current "backlog" is published by Department of State each month:
Most applicants from countries other than those listed can finish their green card process well within the H-1B's 6-year limit, and do not benefit from this proposed rule.