I think it's often expressed with the word next, in place of the now, particularly when it's used to form an exasperated exclamation:
Next you will tell me that Rome isn't even in Italy!
I did a Google books search which revealed several contemporary examples. When I performed a similar search using "now" in place of "next", there were several results returned, but most of them seemed to be in an interrogation setting, not the ironic utterances you point to. Here are a small handful of samples:
"Next you will tell me they are sending aeroplanes to the stars, just like to London."
"Don't tell me fibs" — the teacher sounded annoyed — "why next you will tell me that you speak fluent French."
"Now you will tell me what you really are. You will tell me why you have come here with Lieutenant Halfhyde."
"Now you will tell me what is happening, unless you wish to have me tied to my horse's back and carry me screaming aloud all the way to Cornwall!"
I'm not claiming that the word "now" couldn't be used in this way, but I think "next" might be a better choice.
There's also the idiomatic "Now you tell me," which is sometimes said when someone reveals some information too late:
"Oh! I forgot to tell you! We'll need to go pick up Becky, too!"
"Now you tell me! We'll never get there on time."
'While and When' are subordinating time conjunctions like before, after, ere, till etc. Particularly, these two conjunctions, amongst others, also mean 'during the time that' and connect two events happening at the same point of time. When these conjunctions, or for that matter, other time conjunctions refer to future time in a dependent time clause, we do not use 'shall/will' but stick to Present tense/Imperative. Cf.
You will push the button and the door will open. X. When you push the button, the door will open.
Why?
Broadly speaking, English Tenses rest on Time(when) & Aspect(how) where sequence has a vital role to play. In present and past tense, when & while pose no problems, only sequence is the deciding factor.
The restriction applies to future tense (use of will). Simple present is very common in future references when time of the subordinate clause is anterior to or simultaneous with that of the main clause. Present can foresee near future of firm decision, scheduled action or fixed time table.
So to say, a subordinate clause is subservient to the verb (predicator) of the main clause. Actually, future time is determined by the main verb of the main clause. If the main clause already has future reference, it is not usually necessary to specify this again. There is moreover the question of sequence/ correlation.
- While volcano will erupt, people will take to their heels.X
Wouldn't it be judicious to let the volcano erupt first.
Admittedly there may be situations where it becomes necessary to imbibe future time reference in the subordinate clause also. ln that case we may make use of the peripheries "going to..." instead of an explicit future. But mostly we would stick to the thumb rule of using present tense.
The example sentences with the subordinate clauses in the present are grammatical — sequentially and semantically.
Best Answer
SHORT ANSWER:
Only your first sentence is idiomatic English.
LONG ANSWER:
First, will is employed in when clauses only if when is employed as a relative adverb, not if when is employed as a subordinating conjunction:
Second, the ‘sequence of tenses’ rules for sentences with [when] ... [then] and [if] ...[then] constructions are very similar, so I’ll treat them together.
The rules vary depending on whether the sentence expresses habitual practice or, as in your example, a single contingency.
If the sentence expresses a repeated or habitual practice, both clauses will have the same tense: either simple present or simple past. In these cases, [when] or [if] bears the sense whenever.
When the sentence deals with a single occasion, English employs a sequential structure, in which the [then] clause is depicted as ‘following’ the [when] or [if] clause. In practice this means that
In sentences with present reference, a simple present or present perfect in the [when/if] clause is paired with a will + unmarked infinitive construction in the [then] clause.
Sentences with past reference are ‘backshifted’: a simple past or past perfect in the [when/if] clause is paired with a would + unmarked infinitive construction in the [then] clause.