They can do whatever the hell they want. That's part of the allure of being a cult leader. Though I don't think they will, mainly for the reasons already stated here. They'd have trouble selling it, and there are enough of those that are donating that would stop if they push too hard and in the wrong way.
They've already shown their plans on how they're going to try to raise the funds, and they're fairly clever. Things like the congregation-level tithe work perfectly because it puts the pressure on the elders to pressure the members. The elders aren't getting directly beaten up about their contributions, but since they have to give local needs parts and announce the shortfall, many will give more to avoid seeing themselves as hypocrites. At the same time the members see the pressure from the elders as a local issue, not a systemic one and they have their excuse for the hypocrisy.
They're doing the same thing with the assembly hall costs - raising per-publisher rates to create a group debt, then pressuring everyone to pay it off. They're also doing more special events with live streams and ordering that any funds donated at the kingdom hall for those events be sent in to the org. They do a pretty good job of keeping everything a group debt and letting elders do the legwork. They also do a pretty good job of making the R/F think they're actually getting something whenever there's a money grab - assemblies, "forgiven" loans and the LDC handles your remodel, etc. Of course they don't actually get anything, but as long as they create the appearance most JWs will go along because they don't want to see it for what it is.
In line with what Vidiot was saying - they'd probably not make it a DF offense anyway, because the whole point of such a policy would be to get people to donate more, they would probably use punishments that are more easily revoked once it has the desired effect. If you started DFing people for not donating (especially those that just couldn't raise the cash at the time) a lot of those would never come back. If you use social pressure, they'll stick around and start donating when they can.