Reb Eliezer, you said (disingenuously quoting a Rambam which is not halacha l’maaseh) that it’s assur.
The argument isn’t that everyone must learn full time. You’re basically making the same error as Rational. I’m arguing against your mistaken assertion that one may not learn full time and not work. That is simply not the accepted halacha.
I’m just saying that it’s okay (and that’s an understatement) that we have people doing that (כן ירבו), but I’m not saying that everyone has to. So all of your questions, such as what will be with Yissochor/Zevulun, are irrelevant.