I do like these changes. The Second Luriani War isn't needed, the Luriani won't want to be fighting there, committing everything to facing the K'kree. Not sure what to do about Lucan's faction. Perhaps his Admiral see which way it's going to go during Dulinor's advance and off Lucan putting his infant daughter on the throne. Then pull back behind Capitol al la Napoleon.
I think that, even if you try to look at "Lucan" (the faction) through the most rose-coloured glasses you can find, you still have a faction that is motivated by extreme cynicism and selfishness. Whether Lucan (the individual) is a moral monster or not, all of powers-behind-the-throne in his faction seem to repeatedly make decisions and follow policies that only make sense if they are giving that power-broker some sort of payoff, even if that payoff is coming at the expense of the Imperium - or even the faction - as a whole.
So Commodore X "misinterprets" an order from Admiral Y, and as a result, the campaign that Admiral Y is leading fails. Commodore X attributes the blame to Admiral Y, and Grand Admiral Z in High Command sees that there is value in getting rid of Admiral Y who, if the campaign succeeds, might take his job. Grand Admiral Z accepts Commodore X's version of events, Admiral Y is demoted (or shot), and Commodore X is promoted to the vacancy left by Y. Now new-Admiral X and Grand Admiral Z have potential leverage over each other, and each starts to look for how they can sideline the other. And so the dance continues.
In this situation, Lucan (the individual) will lose authority when it becomes apparent that there is no payoff from sticking with him. Only a few idealists who truly believe he is the rightful heir (if any remain by 1130), and any cronies who see that they will be even worse off if they try to defect, are likely to stay by Lucan's side until the bitter end. The loss of Capital, or even the impending loss of Capital, is a clear sign that it is time for the rats to start jumping ship. (See the final week of the 3rd Reich.)
Consequently, any defence of Capital is likely to be confused, and probably ineffective. And any hypothetical organised withdrawal back behind Capital is unlikely to eventuate, because elements of the Lucanic command structure are likely to peel off with their own fleets and try to come to their own terms with Dulinor, or else just head home. Even if some commanders maintain their units' integrity, the desertion rate among smaller squadrons, and individual ships, is likely to be very high.
Hence my thought that the likely outcome in Core beyond 1130 is going to be one (or a combination) of the following:
a) Most of Core (especially defectors from "Lucan") acknowledging Dulinor as the Emperor, but with Dulinor being sensible enough to only attempt nominal authority over the sector;
b) A series of "city-states" based around 1-2 HiPop worlds, perhaps trading successfully, but with none willing to recognise any overarching authority ; and/or
c) A single main "Lucanic" successor state, perhaps nominally recognising La Infanta, but with practical control invested in a council of HiPop world leaders, naval commanders, and any surviving long-term local nobility.
Cheers,
KenB