Yes, a can of worms.
Some points which could be contested in the courts:
1. The Dawes and Curtis Acts were forced on the tribes.
2. The government was supposed to remove the freedmen following emancipation. This was not done- could this invalidate their claims? (most did leave on their own- can they and their descendants claim rights 'in the Tribes'?).
3. The Dawes rolls had ballooned to over 200,000 by 1914 as people with questionable claims were added. The rolls were closed (status of consequent claims?). As John in Kansas notes, by this time the descendants would be astronomical in number. Any claims they made would be worthless financially, as John and others have pointed out.
4. It is my understanding that the Delawares have withdrawn from the Tribes. What would be the Courts response to claims arising with regard to them?
5. There have been court decisions, and tribal decisions on matters of tribal membership, all over the United States and Alaska. These decisions (precedents) must be considered (Don't bring up the subject of Hawaiian monies held by the Federal government).

Who gets royalties on oil recovered on what was once tribal lands?
The answer is those who were lucky in their 40-acre allotments, and oil was/is considered to be from wells on their property, or drawn from under their property (this is much simplified). In any case, anyone who cannot trace their ownership has no claim.

I am certain that Indians across North America will support the right of the Tribes to control membership. Attempts to limit what is perceived as their right will be fought.

Casinos? Some of them are controlled by the Tribes, but how the monies are handled or entailed is outside of my knowledge. The State will certainly fight any attempts to reduce their take.