To be frank, some of the guesses listed above are bizarre. It might be worthwhile for some folks to spend ten minutes researching the history and background of past appointments before pronouncing who the candidate should be. Note: most prior commissioners have not, in fact, been former Chiefs of Department. Note: they will also not simply select from among a group of two chiefs you happen to know the name of.
Here's my two cents: for better or worse (often worse) the current administration has placed such a high value on their DEI initiatives that I would be shocked if the successful candidate does not fit that agenda. There is a former FDNY First Deputy Commissioner who worked his way through the front-line ranks and seems to be very highly regarded by the uniformed members who also happens to be African American. I cannot imagine there are many others who would fit all that criteria. Hopefully they give that option a close look and don't simply appoint another political hack who has no respect for the FD.