Yes.
However, that is broken right now (tested current HBS, HBT, and HBK), because those four (default) parameters are not changed by Foris.
Mhm, you are about stateful and pretend on it. I tested only stateless IPv6. If you really need stateful IPv6, I have a look into that again. However I am curious, what is your use-case for DHCPv6? Here in Germany, DHCPv6 is a dead horse since Microsoft added support for RDNSS. As of today, I am aware of only one use-case and that is Windows 8.1 (or Windows 10 Version 1507 LTSB or Windows 10 Version 1607 LTSB) in a IPv6-only scenario. I thought, you were looking for a Dual-Stack connectivity while your Turris device is a host client, in general.
Well, there is a complete different use case, at least here: You have several Wi-Fi access points in your LAN and the user roams between them, for example a Wi-Fi phone while being in a call. In that case, the Wi-Fi access point must be configured as bridge without NAT. In my case, the Turris MOX(es) are Wi-Fi access points. If there is a DHCP server in one of the access points does not matter actually. Actually, right now my DHCP server is not my router (and my DNS server not my router and not my DHCP server). So the idea is, to have no NAT. My use-case is just about NAT. Again, I am curious, what is your use-case to run Turris OS as host computer?