i just noticed this thread, but i saw the xxi ages ago and then saw the price and forgot about it lol. i thought about it for a bit cos i was getting rebuilding a dt hub and the freehub for them isnt too bad, but the cassette price is a joke.
i dont really see the point of 11 speed, just makes the thing more fragile imo.
main innovation is the 10t bottom cog, which lets you run a smaller ring up front, eg 34/36 and still have a usuable ratio on the flat/downhill
that said there are alternatives
check out the shimano capreo setup for small wheel folders, special cassette and freehub means 9t smallest gear. the only official cassette is 9-26, but i think you can customize it witha standard cassette top 4 cogs, so like 9-32 or 34. i was gonna try if i can find the kit second hand.
in the meantime im using a 10t sprocket/lockring combo from an old moulton, acts as the 8th gear on a 7s setup only though, but thats cool with a 12-32 cassette and a 36t chainring for me
in the meantime if anyone has a hankering for a big sprocket on a budget, check out this guyhttp://stores.ebay.co.uk/mtbtools?_trks ... 7675.l2563
at a push, i see no reason you couldnt bodge that with the capreo setup to get 9-41t on the back.