I found an informative comment in this thread.
I also found information in this page. Look at No.6. To sum it up, indefinite pronouns require de when they are followed by modifiers.
It probably should be acceptable, however those sentences have a subtle difference in emphasis.
- He has some new thing
- He has something new
In the first sentence the emphasis is on the 'thing', the strangeness/incomprehensibility of it. In the second it is on the newness of the object, that he has acquired a new possession.