Adventuredad suggests that I would be able to use a UK seat in the US, and that a UK Isofix base would even work on a US LATCH car seat.
Just to clarify, you cannot use a UK base with a US car seat or vice versa. interchanging bases and seats could be very dangerous. What Adventure Dad meant was that LATCH anchors in US cars are generally compatible with European car seats designed for use with ISOFIX. He meant that the anchors in the car are essentially the same, not that the bases and the car seats are interchangeable. Does that make sense?
in response to Adventuredad's comment that some people use European seats in the US for "additional safety", are the US seats not up to the same/equivalent safety standards?
As the PP explained, there might be some reasons to import a Swedish seat for extended rear facing, especially if you had a child who was very heavy at a young age. I don't think anyone feels there is a reason to do so for newborns or infants. In fact, now that more higher weight rear facing seats are available in the US, most people feel it is not reasonable to do so at all (although Adventure Dad obviously disagrees, as do quite a few other posters here). Even if you were to make a parental decision to import, it would not be legal for you to use a European seat in the US. I for my part happily use US seats in the US and European seats in Europe and feel my child is very safe in both sets of seats.
Would a US seat be compatible with a UK buggy. I see that iCandy is available in the US, and they also have the Maxi-Cosi Mica (which is the equivalent of the UK Maxi-Cosi Cabriofix), but does anyone know if the seat-to-buggy connections are the same?
Some UK buggies will be compatible with US infant seats. It can be kind of tricky to find out which ones are compatible though. I imagine that the iCandy strollers would be compatible with the US Max-Cosi seats, but in general Maxi-Cosi is not as beloved in the US as it is in Europe and I get the impression that their seats are not nearly as high quality here. When I suggested that the Mica was similar to the Cabriofix someone familiar with both seats felt strongly that the Cabriofix is much nicer, for example.
I have a question for you: Do you want to buy a seat for your child on the plane? For me when traveling, especially when baby is very young, this is important, both for safety and for sanity reasons. If you want to buy a seat for your baby on the plane this is what I would personally do:
I would buy the Quinny Zapp and the Maxi-Cosi Mico in the UK. If I remember correctly, the Mico is one of the only UK infant seats that can be installed with a two point belt, in other words could possibly be used on an airplane. I would then avoid British Airways and other UK carriers (who won't let you fly with your baby in a carseat) and fly with someone like KLM who last time I checked were open to European infant seats being used on planes. An even better alternative to buying the Mico would be getting someone to ship you a US infant seat or bring it over for you on a plane (preferably in the original box) that you could then fly to the US with it so that you would already have a car seat with you at your destination and one that is FAA-approved for flight.
I suggest that Zapp because it's a very compact stroller for travel and you can even carry it on the airplane and stow it in the overhead bin. (The 3-wheel European version also has high resale value in the US, incidentally, and it takes the Maxi-Cosi car seats you are interested in.
Then when you get to the US I would plan to buy a convertible carseat, like the PP suggested, so that you are not buying two infant seats. But that's really a personal choice. Since you'll be moving to the US in the winter you might find that you really want to have the option of snapping a car seat into a stroller quickly, if the place you're moving to is a colder climate.
I would personally then buy your big everyday stroller in the US and a car seat that goes with it, if you so choose. (Or if you get a convertible, buy a stroller with a nice flat recline or a bassinet.) You may find that although you like the idea of the Peach the most with your current lifestyle once you move to the US a different type of stroller might meet your needs better. I also wouldn't personally want to spend a whole bunch on a stroller like the Peach and then risk getting it damaged during the trip and have problems accessing my warranty once in the US because I bought it overseas.
All that advice works under the assumption that you want to buy a seat for your child on the plane. If you don't want to buy a seat, I would not even bring a car seat with you to the US. You don't want to risk the damage to the seat of checking it and you'll have enough luggage anyway. Because British airlines don't allow infants to ride in car seats they often have very nice bassinets that you can sometimes reserve in advance. If you are not buying a ticket and thus not bringing a car seat I would personally bring the baby in a baby carrier since the baby will be very young. (Get a really good one and learn how to use it in advance.) Then you have your hands free for your other luggage and tasks. This would assume though that you either don't need the car seat as soon as you get to the US because you can get where you are going using public transport or that you can have someone in the US meet you at the airport with a car seat.
I hope this was helpful and not too overwhelming! There are so many possible ways for this scenario to work. When making similar choices I decided to buy a seat for my child on the airplane and to use legal seats in each of the countries where I was living, but it's really a very personal choice and of course there are financial constraints too.
HTH.