Oh! that you meant by 'maintainable', I think now i understand. Actually I also do not like a pile of code and I.C.s hardware mixed with each other with out any sense, as a project. My way of work is that
1, Be as much careful as humanly possible at the first time during hardware and software development.
2, During debugging process alway choose/made right tool for it. If you don't, a very small problem of 5 minute debugging will take your days or even weeks or even stop you from finishing the project. (It is happen to me several time until I realize.)
3, Do work as much moduler as possible i.e. divide work into small indepandent modules and make those modules as perfect as possible.

Now what i think you thought is that what i am saying about pin EA and port is kind of a rough idea. Thats true it is an idea but i am very much sure about it as i think i can see all the variables involved in that kind of project. May be in future i will try to make some thing like Mon51 from 89c51/52 by my own self using same idea.