Can't see it doing too great TBH.
LBP has done good numbers down to being heavily reduced in price for over a year. I recall it going for around £12 only 3/4 months after release, not sure if this was done to retailers getting too many copies or not.
Depending when this game releases this year, I can only see it doing 1-1.5m this year and around 2m lifetime.
There are just too many better games being released this year on the PS3 and although there aren't any similar games being released, I can see people spending their money on Heavy Rain, GOW3 and GT5 before Modnation, so it may sell well once it reaches a sub £20 price point.
Prediction (June 12th 2017)
Permanent pricedrop for both PS4 Slim and PS4 Pro in October.
PS4 Slim $249 (October 2017)
PS4 Pro $349 (October 2017)