The only issue with this is if you have to make a change to the test team later in the series for form or injury (after 3rd test for example), the domestic players have been playing T20 for a long time which is not ideal. I think the BBL needs to start later personally. Gives the domestic players longer than a couple of shield games to push their case for test selection.
Good point, but that's pretty much where cricket is at with so many formats and levels. Touring teams have that problem regularly and worse - Mason Crane was selected for the Fifth Test having not played a First Class match for 7 weeks and having not played against anyone at any level for nearly 4.