This is a complete non-story and I'm surprised BBC online is leading the politics page with it given the short shrift it got from David Dimbleby on Question Time last night.
As I have previously said on Ben Brogan's blog, the idea of giving MPs the right to vote on a dissolution - first floated in GB's big constitutional statement in July and now being talked up by Harman - is meaningless.
If a Prime Minister were to come to the House to request a dissolution, he would be virtually guaranteed the support of every MP. No MP from his own party would be likely to defy him, while no opposition party MP would be likely to vote against for fear of appearing "frit."
I suspect Labour are trying to spin this as some sort of sop to the fixed-term Parliament debate. But it is not an alternative to fixed term Parliaments and should not be seen as such.