Actually, you likely be eligible for the the FEIE this year despite moving back this October.
Although you will not be a Bona Fide Resident for US tax year 2020, you may qualify for a pro-rata share of the FEIE from Jan to Oct using the Physical Presence Test. This would apply if you had not been in the US for a total of more than 35 days during the the 365 window from Oct 2019 to the date of your return to the US in 2020.
If this is true in your case, not using the partial FEIE for 2020 would serve as a revocation and you’d not be able to use it again for five years without paying for a Private Letter Ruling (and that could rule against you).
If you plan to return overseas involves moving to a higher taxing jurisdiction, then the FTC approach instead of the FEIE is likely the better choice anyway, even after you move.
