The problem with this plan is that there is no guarantee the share price rises in between. It could fall or stay flat, messing up assumptions as to the final share count. That uncertainty would keep investors away from the initial raise.
FHFA could allay such concerns by nailing down the size (and more importantly, the share count) of future capital raises, but in that case it would be better to just do it all at once.
The second route makes far more sense, especially with the short timeline that Calabria finds himself on. There is a good chance he will be out of his job in late January.