That would been not a problem, the inhabitants number could increased dramatically hence 1848, for example. A develloped Romania could attract for emigration all the vlachs from balkans, ukrain, hungary..., plus other ethnics, in small waves, eager for a better lifeThe fundamental problem with a Romania as powerful as France or Germany are this:
Number of speakers in Europe
German 105 millions
French 70 millions
Romanian 24 millions
Romanias potential are much more limited compared to France and Germany as best we could see the Romanians dominating in a multinational dynastic state, but in modern day that's not the most stable solution.