Given the inordinate level of passion, enthusiasm and comment that the EU referendum has attracted, the absence of blogs in the "EU Referendum" section of the UKNDA site is surprising. So, here's a start.
My concern about SDSR15 is that it was too early and should have been conducted after the EU referendum. My reasoning is that, whatever its result, the future foreign policies for the UK, and hence defence needs, will or should change immeasurably.
If, on the one hand, the nation decides on "REMAIN", then it is likely that we will have to accept, if not embrace, the concept of "ever close union" and the eventual creation of a sort of United States of Europe (USE). At some point along this road, the US would be unlikely to provide the UK with the intelligence and other military support that we have enjoyed uniquely for 70 years. We, along with EU allies, would need to invest in our own capabilities and work towards a USE military. That would surely require a very different SDSR than if the EU vote went the other way.
Should the EU referendum result in an "LEAVE" vote, the foundation for an SDSR might not change much from now in the short term, although there could be sentiment to reduce our closeness to the US and adopt independent foreign and defence policies. After all, there's not much point in disengaging from one union only to engage more fully with another. Again, this would mean having to develop more indigenous capabilities in terms of equipment and, particularly, intelligence.
To my mind, the thing most lacking, whatever the EU referendum result, is what President George H W Bush called "the vision thing". If we stay in the EU, what will/should the UK look like in, say 30 years time - a Texas analogue in a USE or much the same as now? If we vote to leave the EU, will we eventually become the 51st State or a successful and prosperous non-aligned nation? Of course, no-one can say with any certainty what the future really will look like but, unless we have some sort of vision to aim for, a future SDSR is likely to be more tactical than strategic.