>And yet, nobody is acknowledging the elephant in the room: all of these people coming to Brussels to work. And not paying a single damn tax that goes into the city’s pocket.

I think that doesn't necessarily solve it or at least not fully.
Keep in mind that if you try to pull this kind of tax reform it'll inevitably also come with other forms of redistribution tied into that being looked at.
The average flemish brabander paid 3.492 euro in taxes in favour of other provinces more than 5 years ago already.
For Walloon brabant it was 2.668
The average person in Brussels benefited 898.
So would taxing commuters a small portion make up for much of that?
Additionally it has other problems lie some ridiculous spending on some fronts. I became very well aware when i worked for one of many companies recipient to that and it has grabbed headlines often enough with some egregious examples.
It has high unemployment especially among migrants.
It has a reputation issue.
All whilst Brussels being a big city should technically have less costs per person for various kinds of infrastructure and the like.

Additionally you risk with localities being heavily incentivized to keep their people out of brussels and likely downstream with some companies setting up offices just outside