An article on the Warhammer App yesterday has officially said the Sentinels of Terra are completely compatible with the new Space Marine Codex. This is good news, and here is exactly what is said regarding the Sentinels of Terra,
All of this content is completely compatible with the new 'Codex: Space Marines; (though the Planetstrike and the Cities of Death stratagems included in the book are designed for older editions of these rules)
This gives us some hope that other supplements, like Tau for instance will still be compatible in the near future.... and get official statements saying they are.
Here also is a response that Tir Mcdoul on Dakka got
Here is the email.
The supplement book's are no longer available and we have not been made aware of them getting reprinted or of any FAQ updates for them. However it does look like the digital copies of these two supplements have been updated. So if you have purchased the digital copies then you can get the updated information there.
The units most affected by the alternate rules in the Iyanden supplement underwent a significant change to their rules in the new Codex: Craftworlds. While these two books were not designed to work together as such, you and your opponent are welcome to use any rules you like in your own games, if you think it will lead to a more exciting mission. If you do own the Iyanden book, it of course remains a fantastic resource for background and artwork for an Eldar collection.
Should you have any other questions please give us a call at 1-800-394-4263 and we will work to get you helped out where we are able.