Here is what I've come to understand...
We know that he Symbian Foundation was substantially responsible for providing SDK/Tools/documentation for Symbian development, setting feature milestones and release dates, etc.
With no more members aside from Nokia, the foundation is redundant. Moreso, it has arguably mismanaged the product that it delivered and the timelines on which it delivered. The Foundation was a noble idea but with Nokia producing most of its assets and reserving the key product-differentiating assets (services and applications) it developed for Nokia products only while other partners simply sat and waited for software to be delivered, it never really had legs to stand on. Nobody but Nokia really contributed anything to the product over the last couple years and as a result, the product really didn't have anything to offer for other partners.
The more I look at it, the more I think Stephen Elop is doing some very wise work.
The total internal transition to Qt means that Symbian Foundation's tools and documentation are useless. The existing SDK is still out there and it will enable support and development for Symbian^1 devices, which I think will continue to be sold to emerging markets for perhaps a couple more years while some of the more costly parts necessary for delivering Symbian^3 (e.g. RAM, GPU, flash memory) come down in cost to the point that devices are cheap enough to manufacture with Symbian^3 for emerging markets.
Nokia's election to forgo the milestone delivery model and instead deliver software as it becomes available means that Symbian Foundation is no longer needed to set release dates or milestones. Nokia will keep doing all of the work that it was already doing for Symbian^4, it will keep working on its services and software and it will keep delivering them. Hopefully, without the Foundation, it will do so faster than before as well. This is the only part where Stephen Elop has to really step on some toes - jack up the pace.
Basically, as a couple others have speculated, this isn't the end of Symbian. If you believe that, you don't understand. Rather, it's Nokia taking its assets back and exerting control over their development instead of letting some supposedly-neutral third party set the goals and "own" the proceeds while Nokia does the legwork.