This is going to be a disaster for Malta. These people don't fuck around when it comes to damaging the places where they live, and with a population under half a million on tiny island, the place can't exactly take a lot of abuse.
There's so much filthy global money in Manhattan and California real estate right now that it's mind-boggling. And as Malta is a tiny island nation, and real estate exhibits extreme price inelasticity, this sort of thing can happen quickly.
Real estate hyperinflation is a plague that must be fought with any means necessary.
Moreover, Malta is clearly selling this as a means of entry to the entire EU. Few will likely choose to relocate to Valletta.
I suppose the thing with Malta is anyone who was from the EU can already go there.
Malta is essentially selling EU-wide* permanent residency permits and is making mad money out of it. Greece is in dire need of money, and is also entitled to the issuing of EU-wide permanent residency permits, so it makes sense for Greece to follow suit.
* Technically speaking, Schengen-Area-wide.
Which may not be for long if the EU decides it doesn't like Malta selling EU-wide residency permits.
No, it's actually EU-wide. An EU citizenship doesn't grant automatically grants you access to the labor market of e.g. Switzerland and Norway (both Schengen but not EU) but it does to the UK and Ireland (both non-Schengen but EU).
The Schengen treaty only is about to things: No passport checks on the border and joint police work. It doesn't grant any additional residency rights for citizens.