The issue wasn't the radio, it was Tegra not being able to handle switching between 4G and 3G, and then overheating because of it. (an issue the all-qualcomm Thunderbolt doesn't have) Revisions to the LTE radios Verizon uses have not been approved, so the new Bionic won't be using anything new. So there are only two options here:
Originally Posted by Jasper
1) Motorola has worked out all of the issues with Tegra and the LTE radio (extremely doubtful, especially in light of the delay for the Xoom)
2) The 'new' Bionic uses a TI OMAP 4 dual-core processor in place of Tegra 2.
Because they scrapped the original Bionic completely, option 2 seems to be the only reasonable one. If they were simply working through the issues with Tegra, they wouldn't have committed themselves to a new form-factor and improved specifications. Because Tegra 2 would have been an older chip by the time the Targa came out (if thats truly what's replacing the Bionic), I find it hard to believe they would have included it in Targa to begin with. So that pretty much leaves the OMAP 4 as the only possibility.
Motorola also seems to have an affinity for TI OMAP chips, so I'd bet money that the new Bionic has one.