This would be a single furnishing that counts as two flowerpots and contains two planting spots.

The important difference between this and just placing two flowerpots would be that the two plants in the double flowerpot can intercross.

This would mean that players would be able to produce their own intercrossed crops in an apartment, without having to deal with the terrible housing system.
(Yes, this is indirectly yet another "the housing system is bad and you should feel bad" thread. But the double flowerpot is the important part.)