The downside of doing something like that is when you decide you want
This is a sure fit for the situation.
If there is a whole note on bottom staff, only one figured bass is allowed as a vertical stack of numbers (at first glance, perhaps adjustable?), so the numbers could easily go above the upper staff if there are two half notes that would be labeled, for instance. Or the vertical stack could just represent the same thing and the distribution is implicitly understood by order (top->down = left->right).
Fascinating! Going to learn about figured bass at Wikipedia right now.
Even though the meaning (use) may be different, it is worth educating oneself about the historical uses of figured bass, since it was a frequently employed element at the time of the great classical composers.