At least I'm un-aware of such fix, the problem clearly still relies deep in 8.1 (and it's updates) somewhere.
Interesting is, that in my case, I am able to temporarily fix it by running Windows update troubleshooter (stops and restarts BITS and Cryptographic services), BUT after rebooting Windows the problem (Windows Store failed to sync machine licenses. Result code 0x80070490) always re-appears.
I have been contacted privately (by Forum MSFT techies) on this case, but haven't heard anything back from them yet.
Waiting this to be solved.