There is no crippling of the TD10. It's 3D native shooting mode is 1080 x 1920 60i MVC format. If you need 24 fps, you can use the pro version of the TD10, the NX3d1u. While this camcorder may look like your TD10 with the exception of the pro audio section and the front lens shade, it really is different inside in the electronics. It lacks digital 5.1 audio and has additional internal storage plus the 24 fps native 3D mode.
Sorry you had trouble shooting negative parallax images a.k.a. "popouts" in 3D with the TD20. It takes some time for some to understand how 3D works and to get the most from their equipment. The TD20 being a smaller interaxial design, is not the best choice for landscapes and longer shots in 3D but it does fine for its design, 3-4 ft minimum and 15 ft maximum for decent 3D. Don't buy a tack hammer to pound railroad spikes.
In Vegas Pro you can set the preview monitor to anything you wish but when you select the blu ray burn option of 1080 x1920 24p that is what gets rendered from the camcorder's 1080 x 1920 60i video clips. Doesn't matter what your presets are in the settings, SBS or TB full or half. That is only to determine what your preview monitor is showing. The settings in the "render as" templates or the Blu Ray burn image settings is what determines how your timeline will render.
Blu Ray 60p is an option that is available for 720 x 1280.
I don't use AVCHD 2.0 but last I heard that is 60p for only 2D video. It is not a blu Ray standard.
The only way I know to shoot 1080 60p x 1920 or 1080 24p x 1920 native video for 3D is to set the TD10 to 2D and use two TD10's in a paired configuration like you see in my avatar. But, I have no way to play the 1080 60p in 3D on any of my 3D Tv's. Maybe some new Blu Ray players can play that format from a thumb drive but it is not a blu ray standard. Therefore I normally set the paired TD10's for native 24p or 60i for shooting. Regardless of what I shoot, I render everything to 24p for blu ray compatibility. If you follow the SMPTE guidelines for film production in 24 fps, the motion will be pretty smooth, as good as film at that frame rate. There was a bug in the older Vegas Pro v10 that caused some stutter but Sony fixed that some time ago in an update, 10e I recall. .