I can see why the manufacture doesn't? Added cost for a very unique implementation.
I2C mux is a solution if you need multiple same address devices on the same I2C bus.?
What I haven't researched is if the si5351 with higher clock count (8 output variants) with only 2 clocks per VDDO have lower cross talk using 1 clock per VDDO.
Since data shown is load dependent, it suggests that it would be.
Regards,
Gary