Staged (partial) transition of a web application from MVC3 to MVC5 or Core?

Question

ASP.NET

Good day.
There is an information system (web application) ASP.NET MVC3 (in NHibernate bundle).
The application has been working for many years, gradually being finalized, something is being fixed, something is being added, in general, everything is like everyone else)
This business consists of several modules, links in the main menu lead to one or another module. One database is used (MSSQL2014).
There was a need to create a new module in which a bunch of different reports will be generated. And then I thought about it ...
After all, it would be time to switch to a more recent version, otherwise MVC3 somehow became outdated little by little. You can switch to MVC5 or even to Core.
I came up with such an idea - to write a new module on a new technology (for example, MVC5 in conjunction with Entity), publish it in IIS as a separate application, and there will be a link
there in the main menu. Well, then, quietly rewrite all the modules in the same way.
Dear members of the forum, please tell me:
1. Is my idea viable.
2. What is the best and correct way to act in my situation.

Answer 1

Here you need to look at the code, everything depends on a lot: how rights are implemented, roles, how authentication works. There was no identity in mvs3 yet, it was necessary to implement the membeship provider by hand, in what form are you going to transfer it?
And then, why on mvs5, and not immediately on the core?
Without knowing the structure, it's hard to say something unequivocally. But I would probably start a new project in such a situation and just quietly transfer pieces of code into it that can be transferred, and write something on a new one. If you transfer from the tail, then you can run into a dead end when the kernel cannot be changed.

Answer 2

Thanks for the answer. I understood your idea.
If we continue to think about this topic, with such a phased (or partial) transfer of the project, one may encounter three main blocks of problems:
1. Authentication / authorization problems.
2. Problems of compatibility of the level of the server software environment. The libraries used in the project are designed for their version of .NET. Those. the bad option is that
you may need a separate server.
3. "Without knowing the structure, it's hard to say something unambiguously." Let's just say, problems of structure. (How strongly interconnected / intertwined logic, data, representations
in different modules, etc., etc.).
Approximately so, or I missed something?