While I cannot speak directly to the concerns you have listed I can say that this step will be a good one for both IMBA and Cambr. IMBA will gain a large membership base that will help its national campaigns while Cambr will benefit from IMBA's structure. You do not have to select that you wish to be a cambr member when you sign up for IMBA, you can remain unattached or you can simply join cambr. There will not be 3 or 4 different cambr chapters to choose from.
I recently moved to Illinois and find myself living INSIDE the city only blocks from Wrigley. I will be working with Cambr on grant writing and sponsorship work. Trust me, I would love to see trails for Mountain bike specific actions within city limits, and I can agree that wider publication of Cambr within the city would be great. In the mean time, a big step has been taken and they are becoming part of IMBA in the most direct way possible. That should be celebrated and, due to it, their abilities will likely grow over the coming years, hopefully to a point where in city work will be attainable.
Speak, Build, Respect, Ride. Pretty good motto i believe.
What i am saying is IMBA members, when they sign up for IMBA, have two options. They can join Cambr, which will show up as an option. Or they can remain unaffiliated. They don't have to join Cambr to join IMBA but if you want to join Cambr you will have to join IMBA. Does that make sense?
As far as it being broken down into multiple regions within Cambr, I can tell you thats not an uncommon feature for larger bike clubs throughout the US.
In any case its certainly not my position to defend the operating system of Cambr, being the newbie around here. I can say that they will have to make some changes with IMBA chapter status and it will take a bit of time to work around it. As I always say, if you wish to see change come out to meetings if you can or be involved in some way. Everyone deserves a voice if you are a member, and thats the way it should be.