As far as I know there is never any mention of any rules about changes to the house system. However, when we look at the reason why the four houses exist, we can see that there would be no point of creating additional houses.
The underlying premise of the question here seems to be that the houses are simply tributes to great wizards and witches. If that was the case then indeed it might make sense to expand the pool of great wizards and witches that are tributed by the houses. However, I think the evidence from the books provides an entirely different reason for the houses.
The reason for the houses (and their names) is not to honor the people they are named after. Rather, the houses were created out of practicality. Hogwarts was co-founded by four individuals: Godric Gryffindor, Helga Hufflepuff, Rowena Ravenclaw, and Salazar Slytherin. These four individuals had different educational philosophies. In order to cater to each of their viewpoints, they divided the school into four separate parts. Essentially there were four separate schools within the school. Each founder chose the students he/she wanted to teach, and presumably taught them what they wanted to teach them. It is possible that a Gryffindor student and a Slytherin student would end up receiving very different educations. Here are the quotes from the Sorting Hat's songs that illustrate this:
From Order of the Phoenix:
These differences caused little strife
When first they came to light,
For each of the four founders had
A House in which they might
Take only those they wanted, so,
For instance, Slytherin
Took only pure-blood wizards
Of great cunning, just like him,
And only those of sharpest mind
Were taught by Ravenclaw
While the bravest and the boldest
Went to daring Gryffindor.
Good Hufflepuff she took the rest,
And taught them all she knew,
Thus the Houses and their founders
Retained friendships firm and true.
From Goblet of Fire:
Now each of these four founders
Formed their own house, for each
Did value different virtues
In the ones they had to teach.
By Gryffindor, the bravest were
Prized far beyond the rest;
For Ravenclaw, the cleverest
Would always be the best;
For Hufflepuff, hard workers were
Most worthy of admission;
And power-hungry Slytherin
Loved those of great ambition.
While still alive they did divide
Their favorites from the throng,
Yet how to pick the worthy ones
When they were dead and gone?
'Twas Gryffindor who found the way,
He whipped me off his head
The founders put some brains in me
So I could choose instead!
When the founders realized that they would eventually die and no longer be able to divide up the school in this fashion, they bewitched the Sorting Hat to take their place. That is to say that the Sorting Hat would divide up potential students in the same way as the founders would have.
Thus, as originally established the houses were not simply a vehicle for fostering team pride, or other such things. The houses had a very specific purpose, which was to assign students to the educational path that would best suit them. Now in the time period in which we see Hogwarts there does not seem to be any real educational differences between the four houses. They all have the same classes, taught by the same teachers, at times even together with other houses. Presumably, at some point in the thousand years between the founders and the time we see Hogwarts, some changes had been introduced. By Harry's time it seems that indeed the houses were nothing more than teams to take pride in, and perhaps a way to keep track of students.
For the original purpose of splitting students by education type there would be no reason to add houses for other famous wizards and witches. The only reason to add houses would be to offer a different style of education, and apparently four houses were enough to cover the different styles. If there were students who didn't quite fit precisely into one category, for all we know they could have joined other houses for certain parts of their magical instruction.
When the system was changed, and Hogwarts became one school with a bunch of teams, the four houses were apparently kept as a holdover from the original system, or as some kind of tradition. Additionally, when the houses are just teams, four is an easy number to work with. With four houses there is sufficient competition, but still a full quarter of the students get to win every year. With four houses each house should have enough students to form a Quidditch team, any other house team or club, provide prefects, etc. If there were ten houses, we might end up with a house that can't field a team, or has no students worthy of being prefects. Four houses also allows the scheduling to be relatively simple; the more houses there are the harder it becomes to schedule classes, sports, practices, etc. without conflict.
There would be no reason to add new houses to honor great wizards or witches, because that was never what the houses were about. Additionally, if more houses were to be added there would certainly be much disagreement about which great wizards and witches should have houses named after themselves. With all the houses being the actual houses established by the founders there was nothing to dispute. Furthermore, once you start adding houses named after recent people, you open the possibility that there might be students who have something personal against the house. For instance if there was a Snape house there might be a Longbottom student who does not want to be associated with the person who bullied Neville for so many years — even if the house is an otherwise good match. So logistically it is just much simpler to keep things the way they are.
Finally, there does seem to me some general reticence in the Wizarding world to change. Aside from some broomstick improvements it seems that they are very much living in the past. Such a society is likely to be one where there would be heavy resistance to such a monumental change as adding new houses to Hogwarts. In the words of Professor Umbridge:
There again, progress for progress’s sake must
be discouraged, for our tried and tested traditions
often require no tinkering. A balance, then, between
old and new, between permanence and change,
between tradition and innovation..."