the way i see it, the proposal has two main values for consideration: architecturally, and intangibly (i.e. related to international sports in general).
between these two, i think that the nomination has a stronger change to be nominated for its architectural value.
in terms of intangible property, for sure it will be compared with the olympia world heritage site. but ultimately, i feel that the two site are incomparable, olympia is related to the ANCIENT olympic games, while the munich stadium was used for the MODERN olympic games. and there is a clear distinction here: whereas the ancient games is a pagan rite and any acts of aggression is literally suspended for the duration of the games, the modern version is more secular, and the ideal of peace is more symbolic (i.e. more applicable between athletes competing within the games, but acts of aggression may continue outside of it, which could be demonstrated by politics stepping over the lines in some editions of the modern olympics). further, the years of the ancient olympic games (i.e. olympiad) have become means of counting years in ancient times, again highlighting its importance as extending beyond sports.
comparing the olympic stadium with venues of modern olympic games, for sure the 1896 athens site will rank higher since that is where it all began. the statement above of "The development of large scale international sport has been illustrative of increased movement of people since the late 19th and increased 'leisure' activities" is more apt with the 1896 site, connecting more with the ideals of coubertin. the munich venue came after, in the mid-20th century. and with respect to this period, there are a good number of venues that have become emblems of their sports--being known as the cathedrals and meccas of leisure and sporting entertainment, like maracaña and aztec stadiums for latin american soccer, sw19 for tennis, and several other european stadiums. as the site of the olympic games, the berlin stadium may even be ranked higher (it held the first games in germany). aside from this, any intangible value of the place related to the merit of the olympic games might be forever overshadowed by what happened outside of the games, as usually recounted in documentaries, history books and sports reviews.
architecturally however, it's a different story. the stadium is always recounted in architecture books, especially for the design of the roof. i'm not really familiar with the details, but experts might provide further justification on the site's importance not just in terms of its aesthetic design but also its structural engineering.
so with respect to all these, i have reservations on the site's qualitification on the basis of criterion vi if olympic games will be the main point of justification. related to this, it might not be appropriate for this to serve as an extension of the olympia site, which represents the ancient version. the commonality of the two is the ideal of achieving peace through sports, but i think that this is better displayed in the 1896 site for its association with the vision of coubertin and as the first modern olympic games. however, a serial site just encompassing all sites of modern olympic games might be probable, considering that they are all roughly from the same period (from late 19th to 20th century), hence, showing the development of the modern olympic ideal, as well as the evolution of stadium architecture in the contemporary era. if it gets inscribed on the list for architectural value, an extension to an existing world heritage site might not even be a necessary arrangement, since this monument might have value significant enough to stand on its own on the list, with the likes of the great wall, stonehenge, and even olympia.