Yes, you can still make the 645 election. All the ones I've had recently, both the trust and estate already had an EIN by the time I got involved; I'd have to re-read the instructions to see if you need to get an estate EIN as well as the trust EIN.

The advantages I see to the election are: 1) better chance that you'll be able to file a first-and-final return and 2) the benes get an extra year to pay the tax. I hate fiscal year entities that are ongoing; they need extensions at times I'm not thinking about extensions, and guesses as to how much of the dividends will end up being qualified.

If it were my client, my advice would be to try to get everything wrapped up by 12/31 if possible.