I do intend to return to the UK. But I gave no specific date of return - I left it deliberately open-ended because I had some notion that I wanted to use the opportunity to test some principle, though not specifically this one. I thought maybe I might go to Ireland from NL to see if the Irish try to register me on their own SOR.
As I understand it, I have to sign on upon returning regardless of when I return.
I have been abroad before and nobody was interested in examining my passport when I got back (it was within Shengen\Continent).
I have both business and personal reasons for wanting to visit the US (I have a lady friend in Maryland looking after her sick father and she gets lonely out in the sticks), but none are so spontaneous as to merit a trip right now.
Well it all depends how much the police care. So, do they feel mucked about if you go to the US or do they gleefully wash their hands of 2nd ports of call they don't know about (somebody else's problem, knowledge is responsibility etc).
I know spontaneous 2nd ports of call in general are not problematic, not even informally. But leaping halfway round the world makes the first port of call look like a front for the 2nd, and in this case it is the British police who control my access to the 2nd (had it been the 1st), so you're messing with their agenda if you get through by making it a 2nd. But I wonder if they care.