Matlab is good for fleshing out system performance and designing system mockups prior to prototyping. It is NOT viable for production systems.
Matlab is really good for the following:
- Imaging problems/systems
- Control systems and design (simulink)
- DSP, filters, and linear systems
- Physical optics and light propagation
Matlab is ok for:
- Machine learning/classification problems
- Regression problems
Many companies use Matlab, especially for optical system/image processing mockups and control systems. I personally used it a for a contract with a large orange grower for a fruit defect grading prototype (in addition to C++ and other optical modeling design software like FRED, ZEMAX).
Your biggest issue will be finding clients, but Matlab is particularly prevalent in the aerospace, defense, electrical engineering, applied mathematics, and optical engineering communities.
Note that, if you are not a US citizen, then contracting with US aerospace and defense companies will be quite difficult.
Your second question was about the financial part. Really this heavily depends on your overall expertise, not just your Matlab knowledge. For instance, I have already written entire packages in Matlab for light propagation, and for light polarization modeling. Now that these are finished, I can use them for all clients and charge them accordingly. If you wanted to charge a single client to build something like that, it would be very costly. Also I have a lot of experience using Matlab on optical and optical systems problems. Given this background, I can charge very good rates.
The answer to the financial question is maybe. What other expertise do you bring to the table? What kinds of custom software do you have in your own toolkit? You will need to use yourself as an entire package to determine a rate, then decide if it is viable. Please also take a look at my answer here for general advice about freelancing rates vs employment salaries.