It should be kimchi under the official consistent romanization scheme. I'm told that gimchi is actually closer to the correct pronunciation. But yeah, I would really expect to see it spelled kimchi in a textbook.
In other other scheme (Yale romanisation, the old romanisation, Japanese kanaisation, North Korean romanisation), the k/g, p/b, t/d pairs get switched to the first because its a pure sound at the beginning of a word. Elsewhere in the word it somewhat gets mutated into the latter. My ears would confirm this too (although I noticed variance by region). Level of aspiration (k vs kh) is far more important anyway (yet the new system ceases to mark that explicitly , sigh). "G" is the official under the new system, with the exceptions being companies
that already were registered pre-2000 and thus have an international reputation abroad (think Samsung). For them, making the switch is only encouraged.
Note that the new system only had consistency and ease of conversion in mind, as opposed to accuracy.
When Korea is striving to be recognised internationally as a travel destination and popular cuisine, changing the spelling of its most famous culinary product seems utterly foolish to me personally.