The term National Liberal has been used before. Followers of Lloyd George stood in the 1922 general election as National Liberals, without Conservative opposition. This first Liberal National Party only lasted until the following year, when the Liberal Nationals and the Liberals reunited before the 1923 election.
The term re-emerged in the 1940s when the Liberal Nationals swapped to being the National Liberals. The Liberal Nationals were a group which started to break away from the Liberal Party in 1931 after the formation of the National Government. By 1933 the Liberals and the Liberal Nationals were on opposite sides of the Commons. The Liberal Nationals became closer and closer to the Conservatives, agreeing an electoral pact in 1947 and eventually being subsumed fully into the Conservative Party in 1968.
I suspect that Nick Boles, who read Philosophy, Politics and Economics at university, is fully aware of the history. But I think that he may be choosing to read the history backwards. He is probably starting from the tempting thought (for the Conservatives) of being allied with, and perhaps later taking over, this new party.
However, in the previous examples the Liberal Nationals had split from the Liberals. In this case, Nick Boles’s idea could end up creating a break-away group from the Conservatives – and who knows where they could end up?