I have a bunch of mcpe 0.4.0 worlds, and I wish to use them in 1.1.0. Would they work in that version? I WILL BACKUP.
Generally you can use worlds across versions (unless it specifies in an update log that previous world versions will no longer work, but this usually only happens in Modded Minecraft). However regions that have already generated will not change, and expect items/blocks to change/dissapear, but also remember it will be harder to find blocks/items from the newer versions.
While I am mainly a PC player, loading new chunks for the first time in the new version should load the new versions blocks/items.