Is that really feasible?

We believe it is;  although it's a large sum, when put in perspective it's not an unattainable number.  Considering that all commercial games are ultimately financed from the same source (individual sales), and manage to recoup amounts far beyond their initial budgets, it's not unreasonable to think a community game could do the same.  In fact, since almost all of the project's revenue will go towards development (as opposed to commercial games, where retailers and publishers take a large cut) it's actually possible to assemble a bigger game budget from fewer people.
 
It's also worth mentioning here that there might be other avenues of funding for a non-profit project like this one: academic or research grants would be one possibility, corporate sponsorship or advertising another.  The bulk of the financing however, will ultimately be from individual contributions: pledges and donations.