`misc:typo` has been in xkb for about 15 years. There's also xkb-birman (matching the current state of the project that inspired all of it). If your national layout does not have level 3 and 4 symbols set, those should work straight away. If it does, it is highly likely that they clash, so you need to create a suitable subset. It is highly advised to find like-minded people, discuss the best options, and then gently push the result to upstream to make it available for everyone. After all, it's Linux, if you won't do it, no one will.
