I'd thought for a while that they would eventually bring it to the CDMA folks after a few months...but they seem to be talking as if they've actually made up their minds to be stubborn about not doing so. I'm guessing that the whole "Optimus G is based on the Nexus 4 specs" was their way of telling us "if you are on Sprint and want a Nexus 4, go get an Optimus G instead".
And the Optimus G is probably the best phone for you, honestly, if you want a Nexus 7. CDMA carriers need to get involved in software updates to phones on their network. This means that, just like the Galaxy Nexus on Verizon, the name "Nexus" will become rapidly meaningless once the carrier loses interest in updating it, which will happen about 5 nanoseconds after the sales start dropping from their peak. Then you'll be looking at months, if not longer, before features from the latest Google firmware reach you.
Get a Nexus on GSM. For CDMA, buy something fairly hackable and root it from the get-go, or accept that the firmware is going to get old very fast.
So if you're going to go CDMA, you might as well take advantage of some of the other carrier-proprietary things like LTE, or non-Nexus-y things like an SD slot, and get one with a replaceable battery.
Which is more important to you? A specific hardware feature, getting the latest software, or coverage?
If your only local coverage or your preferred carrier is a CDMA carrier, don't bother with a Nexus even if they offer it. Honestly. You won't get software updates that much faster, and you'll lose the availability of other hardware features like replaceable batteries and SD slots. If you are dependent on the carrier for software updates, you are going to have taken the other hardware compromises for little return.