dhcpcd is a pretty good alternative. Well maintained and popularly used by many. I used it in a plain Linux router project and it was good enough for my use cases.
Dec 22 2020
Yeah also it looks like wide is hardcoded to support only type 1 DUID (LLT) anyway.... so probably it wasn't accidentally "forgotten" in 1.3 migration that someone probably has realized it wasn't viable to support it... Thanks :)
Sorry I am confused. I took a brief look at the code of dhcp6c and it appears manually modifying the dhcp6c_duid file should be able to keep the change persistent: https://github.com/jinmei/wide-dhcpv6/blob/24ee2a4f0009bc6ac9bd0b7b737aef93a4aa9905/common.c#L992. Did I miss anything? Thanks :)
Dec 21 2020
Accidentally deleted the comment. Is there plan to migrated to dhcpcd instead? dhcpcd has good ipv6 support and being actively maintained too. Thanks.