I was only saying the same thing last night to a mate.
Play the shield completely over and done before the BBL. start in either 1st week on October, or even the last week in September and end it in late December, then straight into the BBL. The BBL is done and dusted by the end of Jan, so that is when we have the Matador Cup. Feb rather than October. Can do same format.
If they need to start the Shield in late September, then they could take the first game to the country areas as the SCG, MCG etc will be sill being used for footy finals.
NSW are playing a game in Wollongong this year, that game could be the one in September instead of Feb which it is this summer. QLD could use Cairns, and VIC used Alice Springs and Junction RD before, SA have used Glenelg.
Using this formula, the test players would get three or four shield games in BEFORE the first test (providing they don't play any more away Mickey mouse ODI tournaments where we send third string teams and get flogged 5-0 again).