It never hurts to call and ask. There have been reports on some sites that Marriott allows this once, but only once, per member. You have to realize points have more flexibility and are offered as awards for far more stays than the certs required. Someone could previously get certs worth 50k points (2 Cat 5 stays) after staying a few nights. 50k points was the offer for people staying 25 nights, so it would not behoove Marriott to allow those with just a few stays to cash in the certs for the same award it was giving to those being asked to stay 25 nights. If you wanted the points, you could have asked to be switched to that offer and stayed the 25 nights. You are, essentially, asking for the award without staying the required nights.
With that out of the way, though, there is no harm in asking. You definitely won't get it if you don't ask, and will be no worse off if you ask and are told no.
I've never heard of this happening and doubt it will.
A cat 1-4 Certificate is intrinsically less valuable than it's supposed 20k points equivalent because:
1. Certs expire, points don't.
2. Cat 1-4 certs have a variable value and redeem for as little as only 6000 points (cat 1 on a pointsaver) to as much as 20,000 points.
3. Points contribute to lifetime totals, certs dont
4. certs can only redeem at less attractive venues, points can (when adding extra points) redeem at any highly valuable property.
I have heard in the past that Marriott has extended the validity of soon-to-expire certs on request. But that's about it.
Hey marriottjad, I've got an answer for you. Looks like free-night certificates cannot be replaced with points. They don't have a point value so you should use the certificate before the expiration date. Hope this helps!