Here's how my thinking goes. We have two goals that will sometimes conflict:
- To have clear and comprehensible posts that allow the greatest number of people to learn
- To respect and accommodate the diverse religious beliefs and practices of our community.
So to a large extent we do want to accommodate the religious practices of our users for how they refer to the divine being. So, for example, for the Tetragrammaton, you'll see all of these in our posts:
- YHWH
- Yahweh
- Jehovah
- HaShem
- The Lord, The Lᴏʀᴅ, The LORD
All of these are acceptable, except perhaps the use of small caps because it's using unicode and may limit the ability to search etc.
Individuals may have personal practices that differ from any of these. I know of at least one Stack Exchange user who really doesn't like using capital letters. It is appropriate that their posts be edited. Likewise idiosyncratic punctuation (for example, putting spaces around every punctuation symbol), or unintentional typos, are almost always fixed.
Some uncommon practices are acceptable. If a Muslim user on this site wrote "Jesus (PBUM)" we'd allow it, but if a Jewish user wrote "the false prophet Jesus", that wouldn't stand. These are common sense examples, and I don't think anyone would disagree.
For the Tetragrammaton, if someone wrote "yahweh", "jehovah" or even "Hashem", most of us would probably consider them typos or lazy capitalisation, and would edit it. While many people prefer the name "Yeshua" to "Jesus", if someone was to use a very obscure transliteration or to invent their own, it would be appropriate to question their use of it in a comment.
So to the specific case asked about. Personally, I don't like either, and I find that both disrupt my reading. But "G-d" at least has a long history of use by Jews. If a Jewish adherent wanted to use it I think we'd have to allow it. "G d" does not to my knowledge have any substantial history of use, and appears to be a personal innovation. It may make break some search systems when you want to search for a quoted phrase. Google's search engine is magic, but I don't know if even it would handle this. It almost certainly would be sub-optimal for screen reader users, as it breaks one word into two, and would be read out as two single letters. Jewish screen reader users may have configured their systems to read out "G-d" as "God" but they would not have for "G d". And if a regular space is used rather than a non-breaking space then the G and d may appear on different lines (here's a real post viewed in the site's mobile version):

For these reasons, I think it is acceptable to fix titles containing "G d" at least, possibly main posts too. But if there is a significant community who does this practice, that would be enough to make me reconsider.