"The fund shall be used exclusively for the purposes of subsidizing the cost of higher education, early education and child care for lower-income and middle-class residents of the commonwealth."
https://malegislature.gov/Bills/193/H2824
Now, money is fungible so, just like with lottery revenues that are devoted to "education spending" in some states, it could be the case that it won't in fact increase net spending for the designated purpose, since what would have been spent on this purpose will end up being redirected.
On the other hand, the projected tax revenue is so large (>5% of Massachusetts's entire annual tax revenue), that I suspect it would end up being a net increase in funding for the stated purposes, even accounting for fungibility.
The projected revenues from this are way larger than what's currently being spent on that purpose, so in that sense, there's no risk of "redirection" - if the projected revenues come to pass (which is likely, as a tax on an endowment is pretty easy to forecast) then it will result in an increase in funding for that purpose.
The chances that they would use that to cover undergraduate education is pretty low. Would 100% go towards other political causes - I have little faith in our political class doing that or using it effectively.