For example, the Google data center in Hamina directly employs about 125 people. The taxes are limited to salaries, power, etc. I'm pretty sure (although didn't check) that the data center is not turning a profit, even though it probably does generate a tremendous amount of money for Google.
Yes, this vision has been thrown about, but they thing is, even if the wildest predictions were to come through, the employment generated by these large-scale datacenters is a small fraction of the jobs lost in other industries. And most of these jobs are relatively low-paying ones such as perimeter security, replacing faulty servers etc. A far cry from, say, the hordes of engineers employed by the telecom sector during the boom years.
Sure, they may indirectly generate a lot of jobs, but you don't need to live next to (or even in the same country as) an Amazon, Google, or whomever's, gigantic datacenter in order to use it.
But converting factories to data centres would be a way to avoid demolition, and create a demand for specialised tech knowledge and make Finland somewhat relevant to the internet, which is what the government is after.
If this change were to pass, however, there will be little internet related tech locating to Finland, which is what the government is actually hoping to happen.
Also of interest are the reasons behind the proposed change. There has been little to none "national security" issues in Finland, so it's somewhat odd to see it pushed as the main reason.
The director of the surveillance police has actually stated in the past that they rely a lot on information passed to them from other surveillance agencies, and that they don't really have anything to give back. I think this is more about amassing data for exchanges between agencies, rather than an any actual threat.