Le Penn will be the first to speak out against the UK if it suits her populist demographic. You are taking a big gamble here on the good will, the good will of people who are already saying "out is out".
The EU will reform now, to keep others inside and not in the way that you think it will. This again does not bode well for the UK. If the EU appears to be more effective more serving it's member states, the opinion changes fast.
We'll see but i find you're banking on something that won't exist a year from now and the talks will last at least 2.