With regard to blockades, I think we need to recognize that a blockade "only" affects the shipping of resources (neglecting knock-on effects which are not straightforward to understand or predict), not necessarily the resources which are already present "behind the lines" so to speak. Already in Aurora this is true mechanically, as a planet cannot receive shipments of minerals from offworld if it is blockaded.
However, a planet is a very large object and almost certainly has the capability to provide essentials such as food, water, etc. to its inhabitants. In fact this is explicitly modeled through Aurora through the agricultural segment of the population. Compare to historical cases where very often the object of a blockade or siege has explicitly been at least in part to starve the defenders into surrendering. As Aurora stands, mechanically this is not possible right now.
In a hypothetical future version in which agricultural production is controllable and food can be shipped from farming worlds to other worlds, allowing colony specialization in this regard, then blockade-based surrender mechanics make sense as a natural extension of such a system...if a population is starving to death at some point surrender becomes at least an option, likely tied to the racial stats. But for now as long as every population is mechanically self-sufficient at a base subsistence level it is not a mechanic which makes much sense.
I would like to see NPRs offer surrender, not so much due to blockading but certainly if their fleet lies in shambles they should offer surrender to get a better result than total annihilation. However this would require an overall rework of diplomacy so I will have to be patient for such things and meanwhile content myself with SM mode and PvP campaigns.
