I recently emailed Forgeworld to see if they had any plans to do some new Tallarn or Praetorian models in the near future... this was their reply:
"We currently have no plans to make any more Tallarn, or any Praetorian models, however, you never know, it may be something we do in the future.
However, Imperial Armour Volume 11, has Space Wolves , and imperial Guard fighting Eldar, so there will be some new Imperial guard pieces for this book"
I'm personally very excited... If I find out some more I'll let you know!