I mostly agree with the points Mark and Greg have raised. I will write up a more detailed post later but I will just point out now that I think this is going to be way more disruptive than people think.
Servlet is a foundational library that is depended on by thousands of additional libraries. It looks like in maven central alone the official artifact has over 10k dependencies. This is not just a simple change of imports, and bytecode transformation is not a panacea, as it will not help if the code cannot be compiled in the first place.
For example If I have code in a library that expects a javax.servlet.HttpServletRequest and my app has a jakarta.servlet.HttpServletRequest then my program will not compile so runtime bytecode transformation is not a solution. The only way to deal with this will be to either get a more up to date version of the library (which may not be possible), or do my own build time transformation, which is not necessarily simple (e.g. I will likely need my own maven repo to deploy my modified version of this artifact).
From a users point of view I think they will mostly see this as all pain with no gain, especially as many users do not use the Servlet API directly but via other frameworks, so will not see any benefits from improvements.
Stuart