Thanks for the original request, and the reply from another user.
While some words indeed do not have sound, there is more than enough (closing in on 20,000) words with audio to cover any given characters (or combination of characters) ample coverage of the pronunciation.
That aside, I do not plan on adding romaji lookups in any form on renshuu. For the most part, renshuu is extremely un-opinionated in the sense that it lets you more or less choose exactly how you want to study and interact with the contents.
With regards to romaji, though, I decided many years ago to deliberately exclude it on renshuu (outside of the hiragana and katakana learning materials). I've discussed this elsewhere on renshuu, and I cannot fully repeat what I've written before, but I feel *extremely* strongly both as a learner and as a teacher (mainly of Enlglish as a second language, but also of Japanese) for 15+ years that romaji should be strongly discouraged outside of learning the original alphabets.
As the OP noted, you do not "need" to know all the kana in order to move onto words, grammar, kanji, etc. However, all evidence I've seen in my life points to it not being "need", but "unless you want to take more time to achieve less, you should learn them ahead of time."
Japanese is hard, and there is no way getting around it. It takes a significant amount of time to get even basic understanding, but renshuu is focused on long-term learning, and not "learn a few words or phrases for a trip" (although this can still be done). In the long run, fully learning the kana alphabets is a drop in the bucket of time that it takes to learn even a fraction of everything else.
(Again, I am not able to list all of the other reasons - trying to catch up after being away on a trip.)
While I naturally wish for others to agree with me on this, I do hope that you can see *why* I did it - I feel that the way renshuu makes the materials available is the fastest and most efficient way of learning Japanese, and while adding romaji *may* help in niche cases for certain users (especially in the realm of what generates motivation for learners), it would create a net negative impact for learners on renshuu as a whole.
