Online reconstruction and RGB-based reconstruction systems needed

**Describe the solution you'd like**
1. Is it possible for open3D to be operated on online reconstruction scenes such as movie characters record? I am going to make it which would be a base for robots' perception.
2. Would it be better to support open3D to handle RGB images without D to reconstruct the scenes? I would like to make it more widespread.

Although the package is for Intel RealSense cameras, I guess that the two features would be necessary for open3D to be a more standard and modern package in the field of 3D reconstruction.

**Additional context**
- [OpenMVG](https://github.com/openMVG/openMVG) and [OpenMVS](https://github.com/cdcseacave/openMVS) are suitable packages to supplement the gap of scene reconstruction without the depth images.
- [ProFORMA: Probabilistic Feature-based On-line Rapid Model Acquisition](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.480.8901&rep=rep1&type=pdf)

I am glad to assist and contribute my efforts to open3D's progress.