This is a HUGE deal, especially in California, where an estimated 430,000 residents are enrolled in off-exchange ACA policies which are virtually identical to their on-exchange equivalent, with the sole distinction of those enrolled in them not being eligible for ACA subsidies.
With subsidies being beefed up and the 400% FPL subsidy cliff having been killed (for the next 2 years, at least), this means that hundreds of thousands of Californians have just become eligible for thousands of dollars in savings...as long as they transition to the same plan on-exchange.
However, the other major cause of hand-wringing when it comes to healthcare costs these days are deductibles and co-pays...the out-of-pocket expenses which people may have to pay in addition to their premiums. Again, co-pays are a flat fee (usually $30-$50) which you have to pay for many doctor visits, while deductibles are the amount which you may have to pay towards various healthcare treatments/services before the insurance carrier actually starts to chip in their 60-90% of the bill. I don't think co-pays have really changed much over the years, but a whole lot of people feel that deductibles have shot up a lot since the ACA went into effect.