I'll admit it: I'm not quite sure what to make of the Sony Handycam NEX-VG900. Essentially the insides of the A99, including the same 24.3mp full-frame sensor, wrapped in the outsides of the VG30 (and its predecessors). That means it's built around the smaller E mount, which covers only part of the sensor, and requires the use of the bundled E-to-A mount LA-EA3 adapter in order to use lenses that would cover the full extent of the sensor. And while it sounds like a great deal -- $3,299.99 compared with say, $8,000 for the Canon C100 or $5,000 for Sony's own NEX-FS100U, both of which use the smaller but adequate for HD Super35 CMOS sensors -- it's also more limited in some ways, because as far as I can tell, all that extra sensor and resolution will have little impact on the final video.
One qualifier: of course, with the large sensor and a FF lens you'll get more control over depth-of-field and the wider angle of view they confer. Plus, if you want the camera to do double-duty for still photos, you get those at full resolution. Those are nontrivial advantages. (Here's a comparison of cinema camera sensor sizes; the VG900 is comparable to the Canon 5D/1D X in this case.)
But those smaller Super35 sensors offer something Sony's more traditional full-frame sensor doesn't: better color handling during video capture. The C100 uses the extra pixel resolution on its sensor to effectively bin the RGB primaries to obtain full 3-channel 1,920x1,080 frames without demosaicking issues. (Read all about it.)
However, it does use 4:2:2 chroma subsampling like the FX100 and unlike the lower-end VG models (an explanation of color subsampling.) Plus Sony offers 1080/24p along with 1080/60p on the VG900, one of the complaints leveled at the first VG series models -- but, oddly, no 1080/30p. And it will come with gamma and color presets designed for simulating film when shooting 24p.
It feels like this camera is screaming to be hacked: to be able to do something with all the pixels lying fallow and to extend the maximum bit rate beyond the 28Mbps enforced by the AVCHD 2.0 codec. Or am I missing something vital?