Hi Chug, yes I had a short diversion in the middle of the day as well.
As to the arrangements, keep it simple and sister the MAA with the CAA, likewise the MilAAIB with the AAIB. Both must be civilian led, both can be staffed by military personnel, preferably in new branches created for the purpose, as well as civilians.
Now I really like the first bit but less the second bit. The problem with making the leadership all civvy is that personal agendas always come to bear when humans are involved. So I would suggest a 2-3 year rotational post between the CAA and MAA with the deputy always being cut from the other side's cloth. That would see independence. The UK AIRPROX Board kind of does what you suggest on a far smaller scale and I think that it would benefit from having a mix of CAA staff and uniformed MAA staff, possibly FTRS. If nothing else having the civvies investigate the military and the military investigating the civvies would see some neet cross-pollenation of ideas and best practice. Also, both sides could demonstrate further independence that seems to be required.
When you look at the Air Navigation Order, SERA and MAA Regulatory Publications then you see that they are pretty closely aligned. So to see a merger may not be that very difficult - as ever waivers and derogations will be needed for niche capabilities on both sides. Since the Shoreham accident the drafts of CAP403 and RA2335 have become very closely aligned and that shows what could be done. Maybe if the CAA leaves EASA due to BREXIT then a golden opportunity may present itself? (I know they have stated they do not intend to leave EASA but depending on where BREXIT takes us then we have no choice!).
LJ