When Minecraft gets updated to 1.5, won't there be a thing where special chests emit a redstone signal depending whether or not it has been opened? With a bit of creativity and fiddling with redstone, you may be able to figure out a way to, perhaps, spill lava over the chests and land around the chests, making them inaccessible. Or something else cool, like having pistons push blocks over the chests making them inaccessible 30 seconds after somebody has left corn (tripwire/pressure plates on doors that provide exits from corn. Gah, just be creative, somethings gotta work.
I love the skylands idea, in fact i had thought of an idea similar myself involving making an ancient greek sky kingdom with the new quartz blocks, but of course this is quite different from steampunk, so good luck with that
Anyway, just don't make the same mistakes as I did with Breeze (need i point them out?), and as a member of Team Vareide, i'm quite sure you are very capable of making something awesome. Make sure the floating islands look nice, maybe having the stone lead up to a nice curved tip at the bottom of each island. Maybe have vines or waterfalls hanging and flowing off the islands for a nice look. If something doesn't look right, try building it again, taking or adding details where necessary. Just make it classy and original, and don't quit half-way through the job