I will retract my previous post which was derogatorily speculative.
I work with high-speed rotating machinery, but for this application maybe sfi standards would be a starting point for comparison:
http://www.sfifoundation.com/wp-cont...9.2_082616.pdf
SFI standards indicate that the flexplate should be balanced by the manufacturer and spun to 12.5-13.5K RPM for 15 minute intervals until a total of 1 hour run time has been achieved. The part is then to be dye-pen or mag-particle inspected for signs of cracking.
Test bars are also to be broken from the parent material to determine its suitability.
You stated that you are using 6061 aluminum, so looking at the specs:
sfi calls for 35,000 psi min yield strength, 42,000 psi min yield strength and 8% min elongation.
6061 specs call for 40,000 min yield strength, 45,000 psi min yield strength and 12% min elongation.
The only possible issues that I see are balance related and a possible lack of testing. As you are not selling an assembled flywheel, you have no control over the balance of the final assembled unit.
It's probably ok for what most guys are going to do with it. Maybe better than stock. Sure does look cool...