I know there are rules for half-elves and half-orcs in the rulebook.
But what about other "half/half" characters?
Anything from a half-elf that's part halfling (not human) to a half-dwarf, half-gnome?
Unless I have missed anything, all the rulebook offers is the Adopted Ancestry feat. But that still requires you to pick your 1st level Ancestry feat from your "main" ancestry - there's no way to gain any trait off of your "second" ancestry without using up your general feat or waiting til a higher level. You become 90% the first ancestry and only 10% the second.
Are rules for general dual ancestry characters (more like 50/50) forthcoming?
Personally, I find it a bit strange - all the rulebook needed to do, was to make the half-elf/half-orc rule cover every character:
"If you decide your character is of dual heritage, you can select ancestry feats from both ancestries whenever you gain an ancestry feat and you can choose your heritage from either ancestry. You gain telltale signs of both ancestries and if either or both your ancestries have traits (like Elf, Orc) you inherit them. In addition, you gain low-light vision if at least one ancestry has low-light vision or darkvision. You gain darkvision only if both ancestries have darkvision."
Please feel free to point me to an existing discussion if you feel it would be helpful.
Yes rules for other(non-human) halves will be in the GMG.
It will likely be the same way it works for Half-Elf and Half-Orc for Humans which works fine.
Do you mean there will be special ancestry feats for every combination?
Assuming an average of four feats per ancestry pair (there's three Half-Elf and five Half-Orc ones), that's sixty ancestry feats. Add another eighty when Hobgoblin, Leshy and Lizardfolk are added.
The Core book already covers adding the half elf and orc to other ancestries. Just says can be rare and ask your GM.
As for others it would be nice but I doubt we will get official support. Probably the best would be house ruling for half gnomes says based on what elves and orcs got in their half ancestry.
Say you wanted to be a half-gnome/half-elf, for example.
Simply take the gnome ancestry and the half-elf heritage. You will have the gnome and elf traits, and will be able to choose from elf or gnome ancestry feats. Then you're all set.
2E is some well-made, that the only hard parts to playing unusual hybrid characters is 1) balancing for unexpectedly powerful combos and 2) coming up with a name that doesn't sound like a joke for the hybrid ancestry.