There is no license I am aware of in the US required for mining itself.  This may be different for pool operators who's shares may be treated as securities, like stocks - but that is not related to the actual mining. 

This may be some confusion with the New York State's recent hearings on whether a 'bitlicense' is going to be put in place in NY.  But this is a future potential and no license is even on the books yet.  It also appears that such a license by NY is focused on money transmitting and not mining.

True, the IRS has not provided guidance on the taxation of bitcoins and I am not sure that reporting the coinbase of mining income at the time it is awarded is the correct treatment for tax purposes.  I think the accountants and attys. out there can go either way. 

The transaction fees that are included with the coinbase, however, present a different issue to me at least, as these are fees paid by others to miners so that their transaction are included in the block.... this could easily be income for services rendered and taxable when the coinbase is awarded or spendable 99 confirms later......