Here's a list of significant things - maybe incomplete: https://wiki.dlang.org/Differences_With_TDPL
Multiple alias this You can only have one subtyping member currently.
Shared Not all of shared's guarantees are implemented yet.
SafeD@safe (and therefore SafeD) isn't fully implemented. So, it doesn't necessarily work quite like it's supposed to yet.
How much of these are relevant today with 2.077.0?