Again, I went the "safe way" and translated "We eat soon." However, it would be much more natural to say, "We'll eat soon" in English. Here are the situations where we use the simple present: http://www.perfect-english-grammar.com/present-simple-use.html http://www.englishpage.com/verbpage/simplepresent.html
You're quite right. "We will eat soon" is an accepted translation, and if we don't accept the future tense in cases like this, please report them and we'll add them. Swedish uses present with a futural meaning much more often than English does. In lessons that are not about that, we tend to stretch the use of the present tense in English in order to make it easier on learners.
There's no reverse tree (yet), but the main translation must always be used in the reversed sentence. So if I'd change the main translation, the new sentence would show up for people to translate into Swedish, and then they'd think, wait, I haven't learned the future tense yet, help! That's what we're trying to avoid, but you're totally right that will eat is a much better translation here, and it's good that you're pointing it out.