Ok, I got it. I thought that was strange as well, since segwit came out of a soft fork, so I actually expected that the "old addresses" would still be compatible with the segwit ones, but I then heard things about those compatibility issues, and I wasn't fully understanding them.
Nested Segwit (starting 3) will work anywhere, all wallet software understands it. It's only the bc1 addresses that won't work backwards compatibly, and that's kind of irrelevant seeing as there aren't many wallets that use bc1 addresses. So it's all software related, so we just need to wait for wallets to be updated.
Best advice is to use nested 3-starting addresses for Segwit now, because they're completely backwards compatible for all services and wallets. So there's no need to wait for others to wait to update, you can use Segwit now backwards compatibly.
I heard that the new version of Bitcoin Core wallet due to complete by May 1, should help solving these "problems".
No, Bitcoin Core 0.16 will be available something like next week, I would guess. It's the Segwit wallet release, and has been expedited a little.