Should be an EU wide mandate at this point, as it's mostly pros with little cons. Since the options are 1), keep spending EU taxpayer money to boost Microsoft's and other US big-tech market cap, or 2), spend EU taxpayer money on FOSS and local companies implementing and maintaining that FOSS for local infrastructure, then the correct choice seems obvious to me. The only cons are the short term costs, teething issues…
Isn't the Linux/GNU philosophy "Use the best tool for the job". Making OSS always a choice is good, but it is definitely not always the best tool for the job.
Either way, you can't make a rule for people to choose the best tool for the job. A rule like this may come closer to the GNU Linux philosophy.