The reward card limit is set at:
Commons will be limited to 400,000 each
Raress will be limited to 100,000 each
Epicss will be limited to 40,000 each
Legendaries will be limited to 10,000 each
For reference, Beta cards are estimated on pace for roughly:
135,000 for commons
55,000 for rares
12,000 for epics
3,600 for legendaries