PSR can limit what you spend but they are already a billion in the hole at the moment, how much will a new stadium cost on top of that? They can get it mortgaged on the never, never but the payments are another millstone around their neck. A new stadium costs a lot of money to pay off, look how uncompetitive Arsenal went when they moved to the Emirates. Fitting out the Etihad after City moved there nearly sunk the club.
The standard of the rags squad has dropped rapidly over the last few years which reflects with where they are now in the league. Managing a new stadium build which will probably end up over budget whilst trying to build a team to compete for the top four let alone win the title will be a big ask.