The suggestion that a plurality of the popular vote should be sufficient to totally command the government is the same undemocratic lunacy that gave us Trump and it's terrific to see Italian voters rejecting it.
That was phrased a little dramatically, but the point is that I am very opposed to abolishing perfect bicameralism -- in the current Italian system, the Senate can override the decisions of the lower chamber, and functions as an important check on the legislative process, while part of the suggested reform is to abolish this. Under the present system, a majority of the lower-house was elected with 29.5% of the vote in 2013; while the electoral system was changed in 2015 to make this more difficult, it is still possible to win an absolute majority as long as you exceed a 40% threshold, so you can still win an absolute majority even with most of the electorate voting against you (or, in a runoff between the top-two scoring parties, with most of the electorate simply considering you a lesser of two evils).
So, yeah, allowing a minority of the electorate to elect an absolute majority of the lower chamber of parliament and then removing a check on the power of that lower chamber seems very reckless and antidemocratic to me, and I would've voted against this referendum if I lived in Italy. I'm not thrilled about triggering a general election that M5S have a decent chance to win, but at least this way when they do win (since it seems to be a question of when, not if, at this point) they won't be able to singlehandedly enact a bunch of new legislation.
