I think it partly will hinge on how many of those certificates are actually out there.
So far, Marriott has been pretty reasonable in the transition. The certificates are only good for a year (as are free nights) yet they have been nice about extensions. I think most of the people probably trying to 'save' by transitioning their points into Marriott nights and flights are people who were SPG members, many of us who expected a devalued program, and the reality is the program has transitioned well.
I also wouldn't call it gaming the system. It's really about maximizing the value of what you have versus the possible devaluation - similar to when a new
point chart comes out - effective in 2 weeks - you would try to book based on the old chart with your already earned points as when you earned them, you expected them to be worth 'X'.
The one thing about points and rewards is they don't normally gain interest or value over time - usually the point when you earn is their highest value point.
So, if on this one occasion there is a slight hedge against inflation, I don't think Marriott will work very hard to kill it as it's only a temporary gain for a few.