In a recent update in Mike Shinoda's LPC Numb journal, he has said that work will begin on new material after the Projekt Revolution tour is up.

He also talks about some "surprises" for the people who are going to the festival shows and Projekt Revolution dates.

"yesterday, we finished rehearsals for our international and US shows. things went pretty well. we still have some kinks to work out, but hopefully everything will be handled before we play our first gig in the UK. we have a few surprises for you guys...this is going to be our last touring run for this album, so if you want to see us this year, this is the only time to do it. after this, it's time to get back into the studio..."

Source: Mike Shinoda's Numb Journal
Thanks to CLme of the LPU for the news.