(1) A language is not, with all due respect to Max Weinreich, merely a dialect with an army and a navy. An erstwhile dialect is a separate language only if, and only because, its speakers decide it is. Norwegian and Swedish are about as similar to one another as the vernaculars of, say, Beirut and Damascus. Moldovan and Romanian are two names for two different countries' standard languages which happen to be more or less identical (more so than British and American English.) On the other hand, the various colloquial dialects of the German-speaking world are quite divergent, and often mutually unintelligible. Standard German is used as a linguistic coin of the realm. Regarding language unification movements you say:Moreover, traditionally, the small language unification movements that did succeed in producing national languages benefitted from overwhelming, popular support among members of the proposed nation. More importantly, they sought to normalize not prestige, hermetic, (written) literary languages, but rather lower, degraded speech forms that were often already spoken natively by the national community in question (e.g., Creole in Haiti, Old Norse in Norway, and modern, as opposed to biblical Hebrew in Israel)This is absolutely misleading, as even a glance at the Wikipedia entry on "Standard German" would suggest. Standard German originated not as a result of dialect geography, but as a mainly written language learned by many of its users as a foreign language for most of its history. The high rate and quality of education in the German Speaking world allows German speakers to learn the Standard alongside their native vernaculars to such a degree that it is neither odd nor unnatural for a foreigner who speaks Standard German to order coffee or have sex in German without having to make heavy use of a regional vernacular. There are many other standard languages (Finnish, Indonesian, Nynorsk etc.) which are not anyone's native speech, and are even artificial to one degree or another.
2)The comparison with modern Romance is specious and misleading. Perhaps a comparison with the Romance languages & Latin as they existed in late antiquity and the early Middle Ages would be more apposite, if hardly a perfect fit. French and Latin, in the seventeenth century, were already seen as distinct entities. The French elite did not consider French and Latin to be different versions of the same macrolanguage. Certainly not to the same degree educated Arabic-speakers do today. Descartes may have vacillated between French and Latin in writing, but I doubt he would have done so in his speech the way, say, an LBC announcer can vacillate between heavily MSA features (e.g. expressing possibility with a قد يفعل construction) and Colloquial ones (e.g. بعتّلّك اياه for بعثته لك .) For a seventeenth century European to actually speak Latin at length without case-endings and with French syntax, or to speak French with "quia" and "aliquid" rather than "parce que" and "quelque chose" would have been quite a different, and far less acceptable, matter.It is the fact that MSA and the vernaculars bleed into one another in many contexts, often not in terms of discreet levels so much as various points on a gradient, that makes Arabic sociolinguistics quite different from those of seventeenth century France.
3) You mention "Modern as opposed to Biblical Hebrew" in Israel. This bespeaks quite a breathtaking ignorance of Israeli (and more generally Jewish) linguistic history. Modern Hebrew in its spoken form -as it had developed among Jewish immigrants to Palestine in the 19th and 20th centuries before Israeli independence- was not, and never has been completely, embraced as the literary language of Israel. There are several points to make in this regard. But the most salient is this: Any paragraph of Israeli literary prose will contain features (possessive pronouns, verbs in the cohortative and jussive, waw-consecutive etc.) are used in the Bible but are not productive in colloquial Hebrew. Pick up a Modern poem in Hebrew by Natan Alterman or Shaul Tchernichovsky, and this becomes even more evident.