As possible? Of course; nobody can be against that, but people will disagree about what’s possible.

I don’t think that means they should be more narrowly defined than they are now. That would mean a permanent weapons race between those finding and exploiting loopholes and the government, with those having access to the smartest lawyers (= the richest) staying ahead of the law.

For example, if “income” would be restricted to money received in exchange for services, companies would start paying in goods, for example by providing “free” housing, cars, etc. if the government includes such things in the law, companies could start paying out in gold, rather than money. When that gets included, companies could sell special (extremely cheap, no voting rights, must sell when leaving the company) shares to personnel, and pay most of the salary in dividends. That list is endless. Companies could start operating under the flag of Liberia, claim that they don’t pay you for work done, but that they charge you for the use of their machines, and that you sell them the stuff you made with them, etc.