Details are presumably subject to change, but this week's SWTOR community Q&A has a previously un-answered tidbit about the game's free to play shift. Previously created characters will NOT be locked due to their species, though they will be subject to limits on character slots.
(We already knew that no classes would be restricted, so this appears to mean that you can have all of your old characters. I'd also be shocked if they did not offer character slots for sale to non-subscribers. While companies do want to preserve some incentives to subscribe, more slots means more characters, which should in principle mean more revenue, regardless of payment model.)
For players who have their eye on some of the non-human races, this is potentially a significant benefit to (re-)subscribing prior to the changeover and creating any characters that have been on your to-do list. (Personally, I plan to wait for the rumored August world event.) If you are considering trying the game in November and have your eye on a specific race, it might also be worth your while to download the newly unlimited free trial (through level 15) - no promises that these characters will also be grandfathered, but it would seem like spending effort to make sure they slam the door on the fingers of potential customers would be counterproductive.