The standard difficulty will from now on be always between 1 and 0. This is what the PID is programmed to use, and is the target requested by the block at the tip.
1 is the lowest difficulty.
The more leading zero there is after the decimal separator, the more difficult it is to find a block.
The lower the significant figure, at constant number of leading zero, the more difficult it is.
Difficulty zero will never happen, but could be displayed if hashrate reach thousands of GH/s, because in fact the difficulty as displayed by getdifficulty is just a troncated representation of the minimum hexadecimal target to find the block at the tip of the chain, which is a 256 bit number.

I am sure people will get habituated, meanwhile just use the reciprocal, ie 1/difficulty to get an idea.

Otherwise, your miner program will display the difficulty in the reciprocal format.