Hello Guillaume,
you have a point there ... 'Dynamic Modelling' (here: iterative solving of loops) is a much used and appreciated feature in Umberto. It is extremely helpful when modelling process systems with loops and dependencies, as I could experience myself when working with Umberto in a PVC producing plant.
The dynamic modelling feature is definitely on the development roadmap for 2015. There are already two planned Umberto NXT Efficiency releases (the first likely to happen in December 2014, a set of usability improvements), one in Q1/2015. But I can not tell at this stage whether dynamic modelling will make it into the Q1/2015 release.
Are you interested to be a beta tester for this feature in Umberto NXT? Should you wish to volunteer, we would much appreciate it. Please contact me via support@umberto.de