1. Think if I ever take the boat back to the UK, it will be via Morocco or another non-EU state and my location at the time of Brexit or any time spent in the EU quietly forgotten.
2. Would the same strategy work for vessels returning via the Canaries, Gibraltar, the Channel Islands, IOM or any other place with a special relationship with the EU
1. Why would you bother? The HMRC advice makes it clear that a UK resident could bring a boat back to the UK under returned goods relief, if they had evidence of VAT payment anywhere in the EU28. (Incidentally, new information on the CA site goes into somewhat greater detail than the RYA page.)
There's been some concern expressed elsewhere about the three-year limit to RGR eligibility. As I've written before, HMRC's specialist returned goods department has confirmed that "As a private individual, the 3 year rule does not affect you as this is a commercial matter; therefore the 3 year rule would be waived automatically."
2. Again, it's irrelevant. But the IoM is an integral part of the UK customs/VAT zone, so returning via there would confer all the fiscal advantages of returning via the Isle of Wight. In other words, none. (But the kippers are better.).