Converting to anything is more trouble and more expense than just staying with what you have. If it's a technical thing the cost is a lot higher and the risk of breakage is almost infinitely higher.
Without a compelling reason -- like not having a choice -- it makes no sense to switch.
Remember the Y2K problem? Lots of people would rather their apps stored years as four digits rather than two. Until the milage counter ran close to 1999, threatening to confuse software into thinking it had been transported back to 1900, there was no way to justify the cost of rewriting a big chunk of your software just to write 1999 instead of /99.
Until we run out of IPv4 addresses -- any second now -- there wasn't and won't be a good enough reason to switch. No justification, no budget. No budget, no preparation, and damn little planning.
But you still won't catch a break if the migration isn't easy. It's not a new issue, so even without budgets or time, neither the business-unit VPs nor the CIO is going to have much patience with any big complications.
And tell the truth, even without a budget or long-term plan, somewhere you have a thick file of directions and plans and maybe even purchase orders and reconfiguration guides and probably even some internal hosts or address-mapping/conversion tables already running, don't you?
So you're a lot better prepared for real that it looks like on paper, at least judging by the budgets.
I'll be very surprised if it's not very rare for any decent-sized company to have to do a conversion on the fly with its pants on fire.
IT people don't work like that. They fix problems they know they're going to have, and then peel away the problems to reveal the solution that was there under the covers of the old technology.
So those of us without any responsibility for it will sit back and let those of you who do just fix things and let us know afterward. We'll be aware, in a general sort of way, that there's some very labor-intensive magic being done, but we won't appreciate anything but the results.
And if we don't see any difference, meaning you've done your jobs perfectly, we'll assume it was never a big problem in the first place, just like we did with Y2K.
And you'll go back to planning for the next big catastrophe that will never quite happen, for reasons that will remain a mystery to the rest of us unless we find a pile of insanely detailed contingency plans and diagrams and how-tos and emergency procedures in a thick folder or flash drive that's heavy with data and can actually figure out what the network trolls do with themselves all day.