Even if there's not a constitutional issue, yes.
Major himself says:
The absence of a general requirement of legislative prospectivity exists despite the fact that retrospective and retroactive legislation can overturn settled expectations
—but here you might not have the best intentions, but might have reasonable expectations—
and is sometimes perceived as unjust. Those who perceive it as such can perhaps take comfort in the rules of statutory interpretation that require the legislature to indicate clearly any desired retroactive or retrospective effects. Such rules ensure that the legislature has turned its mind to such effects and “determined that the benefits of retroactivity [or retrospectivity] outweigh the potential for disruption or unfairness”.
That's kind of the space I would assume that we're now in.