But like I say, unless you ban Austria from entering Venice R1 it will always do so as long as the alternative is allowing Italy to collect and spend money and place stronger defences on the Austrian border.
One alternative I proposed was this:
At the start of every Italian turn, if Italy is not yet at war, toss a coin. Heads means war, and Italy can do everything an at war nation can do straight away.
This puts Austria in a real dilemma: If it initiates a war with Italy on A1, it gets a start in Venice; but if it ignores Italy for now it might not have to fight on this front for several turns. After all, in 1914 nobody knew when Italy would join in, or even (for sure) on which side.
Italy joining in with the Central Powers produces all kinds of balance issues, but prevaricating about when to declare war is not seriously game breaking.
In a wider view, I consider that each nation has three stages:
1. At Peace.
In this state, units should be distributed evenly throughout homeland provinces, the fleet in home port, and proportionately realistic garrisons in colonies. In the game such a nation collects no income and neither builds nor moves units.
The nation can move its units within home territory in preparation for planned attacks and anticipated enemy movements. In the game, all nations going to war round one get a mobilization turn, the moves of which are written in secret and revealed and implemented simultaneously. On its next turn it is fully At War.
3. At War
A neutral nation which is attacked goes straight to At War status. A neutral nation declaring War (e.g. Italy on I2) must undergo a mobilization first.
Hence, Austria would have to think carefully about bringing Italy into the fight earlier than it needs to.