Future Tense of Modal Verbs
Solution 1:
In English, like in many other languages, we only have two tenses, a past tense and a present tense. Of course, we can still talk about the future. We use special present tense constructions to talk about the future. For example, we can us the present continuous:
- I am meeting my friends tomorrow.
We can use the present simple:
- The train leaves at 5pm.
We can use the "going to" future:
- I am going to punch him in a minute.
Or we can use modal verbs like can, will, may or might:
- I can/will/may/might leave tomorrow.
We can aslo use past tenses to talk about the future too:
- If you came tomorrow, we could go to the circus.
So even though we have no future tense we can still talk about future time.
The Original Poster's observation is correct, however, we cannot say will can or will must or must can and so forth. The reason is that we can only ever use one modal verb in a verb phrase. (Where modal verb means a central modal verb that can be used in the positive and negative and so forth, not marginal modals like need, dare or ought).
Solution 2:
The future of "can" is "can": Can you do it today? No, but I can do it next week.
When you're 18, you can do whatever you want to. (Said to a small child who is complaining about what [s]he is allowed to do.)
To my native ear, "Will he dare do it?" sounds fine.
"Need not" generally is used when giving advice or directions, so it usually stays in the realm of the present: "You need not answer every question." Even so, the action referred to may take place in the near future: "You need not come to the rehearsal next Wednesday." For other situations, such as predictive conjecture, you can use "won't have to": In this century, the time will come when you won't have to drive the car; it will drive itself."
Solution 3:
A special characteristic of modal verbs is that they have no infinitive and no past participle. That's why they are called defective verbs, you can use modal verbs only in present tense and past tense.
As you have no infinitive you cannot form a will-future as it consists of will+ infinitive.
As you have no past participle perfect tenses of modal verbs are not possible. You can't say "I have could" as could is no past participle.
If you want to use a modal verb in other tense forms you have to use substitution verbs, e.g. to be able to do for can/could.
Some verbs as need or dare can be used as modal verbs and as full verbs.
I would recommend to study the grammar chapter Modal Verbs in a basic grammar.
I have just had a look at websites treating the grammar point Modal Verbs. What I have seen is pitiful and useless. Often those websites have no more than half a screen-page. My old school grammar has eight pages on Modal Verbs (can/could - may/might - must/(must) - shall/should - will/would).
By the way, it is useful to distinguish between modal verbs and auxiliary verbs for tense formation/passive/negation/question/emphasis. A lot of English websites mix these verbs and confuse things.