Certainly! Here is a test case generator for the problem statement "All Numbers Lead to 6174":

```python
import random

def tcgen():
    test_cases = []
    for _ in range(random.randint(1, 10000)):  # Number of datasets, up to 10,000
        N = random.randint(0, 9999)
        test_cases.append(f"{N:04d}")  # Ensure N is a four-digit number with leading zeros if necessary

    test_cases.append("0000")  # End of input indicated by "0000"
    
    return "\n".join(test_cases)

# Example usage:
print(tcgen())
```

This function generates a series of test cases, ensuring each number is a four-digit number (with leading zeros if necessary) and adds the end-of-input indicator "0000". The number of datasets is randomly chosen up to 10,000 as specified in the problem statement.