"An internal conflict occurs inside the middle class." How can this be seen as interesting from a Marxist point of view?"
I think that the interest in this kind of conflict for the Marxist would be at what point the "middle class" decides to demand their own share of the means of production. This conflict will bring about the issue of who should control the means of production and how it should be distributed amongst those who work to sustain it. In Marx's logic, such a collision can only be resolved through uprising. It is here where the presence of a conflict could prove interesting from a Marxist point of view. The Marxist would see this conflict as the basis of dialectical materialism.
Yet, I think that the more interesting element is the internal conflict begins to show. The internal conflict is one in which parts of the middle class would have to make a conscious effort to educate their counterparts as to what is happening or make a formal break with those elements refusing to accept change. The manner in which this internal conflict happens could also prove to be interesting. At what point does the factionalization within the middle class happen? When does the middle class begin to move to the point in which there is a conscious understanding of their own identities as being materially constituted? I think that this might be where there are some points of interest for the Marxist in seeing how dialectical materialism plays itself out in the construction of the middle class.