There have been a few posts here on carriers and aircraft - perhaps I can help clear up a few points.
MSOCS - no, Taranis was not required to operate from a carrier. As I've posted often here, the whole business of getting an aircraft on and off a cat and trap ship is extremely difficult, and demands some specific design features and expertise which only the USN really have.
Both Taranis and X-47B were nothing more than flying shapes, and as the F-35 programme shows, getting from that stage to a military aircraft with a usable combat load, range , endurance and speed is a non-trivial problem. It's interesting to note how many people were, a while back, proposing that we buy 'X-47B' as our carrier borne UCAV - less people have commented on the fact that the USN appears to have put their UCLASS programme on hold while they go back and look again at requirements and available technology.
I've posted before on the tendency to assign UCAVs with nearly god-like powers of range and payload, despite the fact that they are still machines governed by the laws of aerodynamics and physics. It's just possible that the USN have determined that, for now, building a UCAV to operate from a carrier with a payload and performance envelope a bit better than a legacy manned aircraft would probably result in a UCAV nearly as big, complex and expensive as a comparable manned aircraft.
On carrier design versus variant choice - it might be useful to remember that JSF (remember that?) actually came first, and the UK's place at the table as a Tier 1 partner on JSF was predicated on two things. First, and most importantly, our STOVL knowledge and a long (over 20 years) history of high level co-operation with the US on that technology. (The MoU under which the UK joined the JSF was actually titled the 'JSF STOVL MoU'). Secondly, the fact that we actually had a requirement, which was (I think) Naval Staff Target 6466, for a Harrier replacement - it was called Future Carrier Bome Aircraft (FCBA). This became Future Joint Combat Aircraft (FJCA) in around 2001, and from where I stood, FJCA was the Tornado replacement.
At that time, as far as I understood, the high level plan for the RAF was a mix of F-35 as a strike asset, with Typhoon as the AD asset. F-35 variant was not specifically identified, but it was my impression that a buy of F-35A was never far away from the table.
UK carrier requirements were framed to include a wide range of aircraft, including FCBA, F-18, Rafale, and even a marinised Typhoon (which didn't actually exist, thus making designing a ship around it a tad iffy). Why not only FCBA? There was some UK nervousness over putting all our eggs in the STOVL basket, but the lack of decisiveness in the UK's carrier design looked worse and worse as time went on. Lack of expertise and an accurate cost model led to the debacle of SDR 2010 and the subsequent carrier design 'hokey-cokey'.
8ter is right on target (as usual) on V-22. My view (and that's all it is) is that the combination of STOVL capability plus good range and endurance will eventually make the case for a UK purchase, especially for SF ops from a carrier.
Hope this helps a bit, best regards as ever to all those building our future land based and maritime aviation capabilities,
Engines