This has come up before for 5e, and the writer (I want to say Patrick, but don't quote me) gave a detailed explaination as to what happened and why, and then the reversal...
To keep it short and sweet (you can go dig for the longer version if you wish):
Deltaware and Regeneration can be combined, in regards to HMHVV..
Not sure what other playable races have regeneration as I am pretty such it was removed from shifters...