I don't see Sony making a new portable console in a at least a decade, here are my reasons:
1Nintendo's 3Ds just smashed the vita sales, probably sony regrets the vita launch.
2I saw a news a long time ago that making games for the vita is kinda expensive, hence most of vita games are not what they could be, this could only scale more in a new console since Sony looks uninterested in making efforts to sell things, eve if this is a more dev related issue it only gets worse.
3The psp had a nice fight with the DS but again the DS smashed the PSP because it had better games, there is no point in making a powerhouse and not using it's power, vita suffers from the same issue, no point in paying for a more powerful console and having graphics like the low end console, look at star ocean on psp! You could get just the same result on a DS!
4Maybe they have learned the lesson with their stupid vitaOnlysdcards, if they again launch a new console and do the same they are risking things here.
5Porting games to the table console is only a faster way to bury your console, sony made this stupid mistake in the same way microgarbage made the xbox content on the pc which kills the idea of buying and xbox. Toukiden, digimon i can name a few games that are not PS4 games but just vita ports, which sux, who buys a ps4 to play vita on the tv?! God i hate bandai.
Don't get me wrong i would love a nice competition against the 3DS and so on but no one wants to enter in the fight, the only reason the PSP did not ended like the dreamcast was because it got hacked pretty soon and it became a very handy gaming device after that, even the vita is now somewhat popular because it got hacked.