Is it possible to "un-exercise" your ISOs? If so, that also gives employees five more years to watch the company trajectory and make a more informed and measured decision -- if they lose confidence in the company, they can return the ISOs to the employer instead of paying an upfront tax bill on what is still somewhat of a lottery ticket.
Seems to me that a key advantage of the deferral period would be if it allowed one to net out the true capital gain/loss if you actually sold or otherwise disposed of (e.g. it became worthless) the stock within the deferral period.