In OP's context, the modal auxiliary verb would establishes the "if-clause" as a conditional, hypothetical scenario. This can be reflected using the subjunctive verb form (plus infinitive)...
It would be good if they were to come forward
...but as that link says, the subjunctive is a special, relatively rare verb form in English - so in practice, native speakers tend to avoid it.
It's often said that English only really has two basic tenses - Present, and "non-Present" (usually, but sometimes misleadingly called Past tense). Because Present tense is more associated with the "real, here and now" world, rather than OP's "imaginary" scenario, we normally use Simple Past...
It would be nice if he came (3310 hits on Google Books)
It would be nice if he comes (1 hit)
It would be nice if he were to come (1 hit)
It would be good if they did that (6740 hits)
It would be good if they do that (3 hits)
It would be good if they were to do that (2 hits)