Again, how many times to I have to bring up that popularity only helped Marth?
Neither Roy nor Ike got in due to popularity.
I already said that Anna getting in this time would only happen as a result of an idea Sakurai came up with himself or through Intelligent Systems.
The thing is that this time Sakurai is faced with a different dillemma than the one he was faced with during pre-Brawl.
During pre-Brawl, Sakurai's problem was that he wanted one FE newcomer, but was unsure who to put in because there had been a whole bunch of new lords created after Roy, so he went to IS for their advice on the matter. They suggested Ike to him, and the rest was history.
With Roy, when Sakurai went to IS for permission to use a second FE character as a clone for Marth, he got a sneak peak at FE6 while he visited, and thought Roy's fire sword made him stand out more than other choices for a Marth clone.
The thing is that:
1. There have only been two lords created since Brawl.
2. Those two lords don't stand out much relative to the FE characters that are already in.
3. There is a strong demand for a FE character that was already cut (Roy), and there would certainly be a very large outcry if he cut another one (Ike).
4. Sakurai (or IS) may want to give FE13 some sort of recognition in playable form.
Aside from Marth and his buddies, no other FE characters get revisited after their two-game arc is done. While, Roy could be revisited via a FE6 remake, or Ike via Priam/Paris, if the story for FE13 is really wrapped up (which it seems to be), then Chrom/Lucina don't have the possibility of being revisited.
Sakurai bringing up the problem of future utility in regards to FE characters (that they end up becoming "old news" a few years after their game is released), could be what leads IS to bring up the idea of Anna to Sakurai, whom is guaranteed to make future appearances in FE games, and will probably have some sort of playable role in future FE game considering she was well-received as one.
However, this scenario is contingent on a whole lot of "what ifs".
The problem is that all of FE13's main actors don't bring anything new to the table, and to just put in a character for the sake of repping FE13 despite the character not really standing out would be a bad move in the long-run for Sakurai.