"When" as a question word can be followed by any appropriate tense. "When" as a conjunction should be followed by a present tense.

By the way, 'when will you come?' is correct grammar but strange.. is there a plan to come already? : 'When are you coming?' or do you want a decision : 'when are you going to come?' In future time expressions, like 'when I..' or 'if I ..' just use the present, without 'will'. :)

I think I understand what you mean. I'd like to say that anytime you ask a future-tense question about an object or person, you should use "When will ......?" .... specifically when you are seeking a point in time "When will .....?" is implying that it has yet to happen and essentially your referring to a future point in time. Example: Future-tense ......... "When will you come home?" Past-tense ......... "When did you come home?" Present-tense that starts with "When......." always leads to an explanation. present-tense ........... "When I come home, I will stop by the store"