If Jeremy Corbyn does become Prime Minister I expect electoral reform, as part of wider constitutional reform, will happen, without the need of plebiscites on the matter. Whilst Labour leaders do say in opposition they favour electoral reform but then ignore it when they are elected, like a brilliant thought during an orgasm, it gets lost in the ecstasy of ‘victory’. I think Corbyn will not do a Blair on the topic of electoral reform.
The chart above, from the Electoral Reform Society, it should be noted that under three other voting systems, only one of them would see the Tories having more seats than Labour, that voting system is AV, the Tories must really regret opposing AV in the 2011 referendum, under AV the Tories would have won an even larger majority in 2015, which may have stopped Mrs May calling a snap election.
The Tories theoretically have at least nearly five years left in government they should use that time to introduce electoral reform before someone else does introduce a new voting system that is detrimental to the Tory party.