There will come a point at which the last MacOS release that supports Intel, will fall off of security updates. Apple tends to provide security updates for 3 years.
Mathworks will stop supporting Intel Mac no later than that time. Mathworks will not run their development systems on an OS that does not have security updates.
Apple typically announces EOL (end of life) in summers (late late spring) -- in particular, they typically announce them in conjunction with the WorldWide Developer Conferences that take place in mid June, since they tend to keep secret until then what new models are going to be available.
My speculation is that the MATLAB release for fall of the following year will not support Intel. On the other hand, market pressure could push Mathworks to stay on an extra year or so.